Wikipedia articles in scope, O
685 articles. Each title links to the article on Wikipedia. Refer to Wikipedia scope for the signals and the rules.
| Article | Signals | Class | Rule |
| O | S4,S5,S8 | | strong |
| O'Brien–Fleming boundary | S2 | Start | strong |
| O'Nan group | S1,S5,S6,S8 | Start | strong |
| O'Nan–Scott theorem | S1,S6,S9 | Start | strong |
| O*-algebra | S1 | Stub | strong |
| O-minimal theory | S1,S4,S6,S8,S9 | Start | strong |
| Oakley protocol | S2,S6 | Stub | strong |
| Obelus | S1 | C | strong |
| Oberwolfach problem | S1,S5,S6,S8,S9 | C | strong |
| Oberwolfach Research Institute for Mathematics | S1,S9 | Start | strong |
| Object of the mind | S2 | C | strong |
| Objection (argument) | S2,S8 | Start | strong |
| Objective stress rate | S4 | | strong |
| Oblate spheroidal coordinates | S1,S5,S6 | Start | strong |
| Obligationes | S2,S6,S9 | Stub | strong |
| Oblique lattice | S1,S3,S6,S9 | Stub | strong |
| Oblique reflection | S1,S6 | Stub | strong |
| Oblique shock | S3,S4 | C | strong |
| Oblivious HTTP | S2,S6 | B | strong |
| Oblivious pseudorandom function | S2,S6 | C | strong |
| Oblivious transfer | S2,S6 | Start | strong |
| Observability | S3,S4,S6 | Start | strong |
| Observability Gramian | S1,S4,S6 | Stub | strong |
| Observable | S3,S4,S6,S8,S9 | Start | strong |
| Observable subgroup | S1 | Stub | strong |
| Observational equivalence | S2,S6 | Stub | strong |
| Observational error | S2,S6,S8,S9 | C | strong |
| Observational methods in psychology | S2,S6 | Start | strong |
| Observational study | S2,S8,S9 | Start | strong |
| Observed information | S1,S2,S4,S5,S6 | Start | strong |
| Observer bias | S2,S6 | C | strong |
| Observer effect | S2 | List | strong |
| Obstacle problem | S1,S4,S6,S9 | Start | strong |
| Obstruction theory | S1,S4,S5,S6,S8,S9 | Start | strong |
| Obversion | S2,S8 | Start | strong |
| OCB mode | S2 | Start | strong |
| Occam's razor | S2,S3,S5,S8,S9 | C | strong |
| Occupancy frequency distribution | S2,S5,S6 | C | strong |
| Occupancy grid mapping | S1 | Stub | strong |
| Occupational Depression Inventory | S2,S6 | Start | strong |
| Occupational epidemiology | S2 | C | strong |
| Occurs check | S3,S6 | Start | S6 near |
| Ocean gyre | S3,S4 | Start | strong |
| Ockham algebra | S1,S5,S6,S8,S9 | Stub | strong |
| Octacube (sculpture) | S1,S6,S8,S9 | C | strong |
| Octadecagon | S1,S5,S8 | Stub | strong |
| Octadecahedron | S1,S8,S9 | Stub | strong |
| Octagon | S1,S5,S6,S8 | Start | strong |
| Octagonal number | S1,S5,S6,S8,S9 | Stub | strong |
| Octagonal prism | S1,S5,S8,S9 | Stub | strong |
| Octagonal tiling | S1,S6,S8 | Start | strong |
| Octagram | S1,S5,S6,S8 | Start | strong |
| Octagrammic antiprism | S1,S8,S9 | Stub | strong |
| Octagrammic prism | S1,S8,S9 | Stub | strong |
| Octahedral cupola | S1,S5 | Stub | strong |
| Octahedral number | S1,S5,S6,S8,S9 | Start | strong |
| Octahedral prism | S1,S5,S8,S9 | Start | strong |
| Octahedral pyramid | S1,S5,S9 | Stub | strong |
| Octahedral symmetry | S1,S5,S6,S8,S9 | Start | strong |
| Octahedral-hexagonal tiling honeycomb | S1 | Start | strong |
| Octahedron | S1,S5,S8,S9 | B | strong |
| Octahemioctahedron | S1,S5,S6,S8,S9 | Stub | strong |
| Octal | S1,S5,S6,S8 | C | strong |
| Octant (solid geometry) | S1,S3,S5,S6,S9 | Start | strong |
| Octant of a sphere | S1,S9 | Stub | strong |
| Octant projection | S1,S5,S6 | C | strong |
| Octavio Cordero Palacios (writer) | S1 | Start | strong |
| Octic reciprocity | S1,S6,S9 | Stub | strong |
| Octomino | S1,S5,S6 | Start | strong |
| Octonion | S1,S4,S5,S8,S9 | C | strong |
| Octonion algebra | S1,S4,S5,S8,S9 | Start | strong |
| Odd Aalen | S1,S8,S9 | Start | strong |
| Odd greedy expansion | S1,S6,S8,S9 | Start | strong |
| Odd number theorem | S1,S5,S6,S8 | Stub | strong |
| Odds | S2,S5,S6,S8,S9 | Start | strong |
| Odds algorithm | S2,S5,S6,S8,S9 | Start | strong |
| Odds ratio | S1,S2,S5,S9 | C | strong |
| Odd–even rationing | S1,S6 | C | strong |
| Odd–even sort | S5,S6 | | S6 near |
| ODE filter | S1,S3 | C | strong |
| ODE/IM correspondence | S1 | Stub | strong |
| Oded Regev (computer scientist) | S1,S3,S8,S9 | Start | strong |
| Oded Schramm | S1,S8,S9 | C | strong |
| Odile Favaron | S1,S8,S9 | Stub | strong |
| Odious number | S1,S5,S6,S9 | Stub | strong |
| Odlyzko–Schönhage algorithm | S1,S5,S6,S9 | Stub | strong |
| Odo Van Maelcote | S1 | C | strong |
| Of the form | S1,S5,S6 | Stub | strong |
| Ofelia Teresa Alas | S1 | Start | strong |
| Ofer Zeitouni | S1,S8,S9 | Start | strong |
| Off-the-Record Messaging protocol | S2,S6 | Start | strong |
| Offered load | S2,S6,S8 | Stub | strong |
| Office for National Statistics | S2 | Start | strong |
| Office of the Chief Actuary | S2,S6 | Start | strong |
| Official statistics | S2,S8,S9 | C | strong |
| Offline private key protocol | S2,S6 | Start | strong |
| Offset filtration | S6 | | S6 near |
| Ogawa integral | S1,S2,S5,S6 | Start | strong |
| Ogden hyperelastic model | S3,S4 | Start | strong |
| Ogden tables | S2,S6 | Start | strong |
| Ogden's lemma | S1,S5,S6,S8,S9 | C | strong |
| Ogden–Roxburgh model | S1,S3 | Stub | strong |
| Ogive (statistics) | S2,S5,S9 | Stub | strong |
| Ohlson O-score | S1,S6 | Start | strong |
| Ohsawa–Takegoshi L2 extension theorem | S1,S4,S5,S6 | Stub | strong |
| OjAlgo | S1,S8 | Stub | strong |
| Oka coherence theorem | S1,S4,S5,S6,S8,S9 | Stub | strong |
| Oka's lemma | S1,S5,S6,S9 | Stub | strong |
| Okamoto–Uchiyama cryptosystem | S2 | Start | strong |
| Oka–Weil theorem | S1,S4,S5,S6,S8,S9 | Stub | strong |
| Okubo algebra | S1,S4,S9 | Start | strong |
| Ola Rosling | S2 | Stub | strong |
| Olabisi Ugbebor | S1 | Start | strong |
| Olaf Helmer | S2 | Stub | strong |
| Olaf Storaasli | S1 | Start | strong |
| Olami–Feder–Christensen model | S3,S4,S6 | Stub | strong |
| Olaus Henrici | S1,S9 | Stub | strong |
| Olav Kallenberg | S1,S8,S9 | Start | strong |
| Old quantum theory | S3,S4,S5,S8 | Start | strong |
| Oldroyd-B model | S3,S4 | Stub | strong |
| Ole Barndorff-Nielsen | S1,S2,S9 | Start | strong |
| Ole Michael Ludvigsen Selberg | S1,S8,S9 | Stub | strong |
| Ole Peder Arvesen | S1,S8 | Stub | strong |
| Ole Skovsmose | S1 | Start | strong |
| Olech theorem | S1,S5,S6 | Stub | strong |
| Oleg Besov | S1,S8 | Stub | strong |
| Oleg D. Jefimenko | S3,S4 | Stub | strong |
| Oleg Izhboldin | S1 | Stub | strong |
| Oleg Lupanov | S1,S9 | Start | strong |
| Oleg Marichev | S1,S8,S9 | Stub | strong |
| Oleg Nagornov | S1,S3 | Start | strong |
| Oleg Viro | S1,S8,S9 | Stub | strong |
| Oleksandr Sharkovsky | S3,S4,S9 | Start | strong |
| Olena Vaneeva | S1 | Start | strong |
| OLGA (technology) | S6 | | S6 near |
| Olga Beaver | S1,S9 | Start | strong |
| Olga Bondareva | S1,S9 | Start | strong |
| Olga Gil Medrano | S1,S8,S9 | Start | strong |
| Olga Hahn-Neurath | S1,S2,S6,S8 | Stub | strong |
| Olga Holtz | S1,S9 | Start | strong |
| Olga Ladyzhenskaya | S1,S8,S9 | C | strong |
| Olga Oleinik | S1,S8,S9 | Start | strong |
| Olga Tsuberbiller | S1 | C | strong |
| Olimpíada Brasileira de Matemática | S1,S8,S9 | Stub | strong |
| Olimpíada de Matemática do Grande ABC | S1 | Start | strong |
| Olinde Rodrigues | S1,S6,S8,S9 | Start | strong |
| Olinthus Gregory | S1,S9 | Start | strong |
| Olive Hazlett | S1,S8,S9 | Start | strong |
| Olive Jean Dunn | S1,S2,S8,S9 | C | strong |
| Oliver Byrne (mathematician) | S1,S8,S9 | Start | strong |
| Oliver Chinganya | S2 | Start | strong |
| Oliver Edmunds Glenn | S1,S8,S9 | Stub | strong |
| Oliver Heaviside | S1,S3,S4,S9 | B | strong |
| Olivetti Summa Prima 20 | S1 | Start | strong |
| Olivia Caramello | S1,S9 | C | strong |
| Olivier Guéant | S1 | Start | strong |
| Olivier Pironneau | S1 | Stub | strong |
| Olivier Ramaré | S1,S8,S9 | Stub | strong |
| Olivier Rey | S1 | Stub | strong |
| Olle Häggström | S1,S9 | Start | strong |
| Olli Lehto | S1,S8,S9 | Start | strong |
| Olli Lokki | S1 | Start | strong |
| Olof B. Widlund | S1,S9 | Stub | strong |
| Olog | S1,S6 | Start | strong |
| Olry Terquem | S1,S8,S9 | Start | strong |
| Olvi L. Mangasarian | S1,S3 | Stub | strong |
| Olympia Nicodemi | S1 | Start | strong |
| Olympic gel | S1,S6 | Start | strong |
| Omar Catunda | S1 | B | strong |
| Omar Khayyam | S1,S5,S8,S9 | C | strong |
| OMDoc | S1,S6,S9 | Start | strong |
| Omega and agemo subgroup | S1,S6 | Start | strong |
| Omega constant | S1,S5,S6,S8,S9 | Start | strong |
| Omega language | S2,S3,S6 | Start | strong |
| Omega-categorical theory | S1,S4,S5,S6,S9 | Stub | strong |
| Omega-regular language | S2,S3,S4,S6 | Start | strong |
| OMEMO | S2,S6 | Start | strong |
| Omen | S2,S3 | Start | strong |
| Omitted-variable bias | S2,S6,S9 | Start | strong |
| Omnibus test | S2 | C | strong |
| Omnipotence paradox | S2 | B | strong |
| Omnitruncated 5-simplex honeycomb | S1,S5,S6,S8,S9 | Start | strong |
| Omnitruncated 6-simplex honeycomb | S1,S5,S6,S9 | Start | strong |
| Omnitruncated polyhedron | S1,S8,S9 | Start | strong |
| Omnitruncated simplicial honeycomb | S1,S6,S9 | Start | strong |
| Omnitruncated tesseractic honeycomb | S1,S5,S6,S9 | Stub | strong |
| Omnitruncation | S1,S6,S8,S9 | Stub | strong |
| Omri Sarig | S1,S8 | Start | strong |
| On Conoids and Spheroids | S1,S8,S9 | Stub | strong |
| On Formally Undecidable Propositions of Principia Mathematica and Related Systems | S1,S2,S6,S8,S9 | Start | strong |
| On Indivisible Lines | S2 | Stub | strong |
| On Interpretation | S2,S8,S9 | Start | strong |
| On Numbers and Games | S1,S5,S6,S8,S9 | Start | strong |
| On Spirals | S1,S5,S8,S9 | Start | strong |
| On the Number of Primes Less Than a Given Magnitude | S1,S6,S8,S9 | Start | strong |
| On the Sphere and Cylinder | S1,S5,S8,S9 | Start | strong |
| On-Line Encyclopedia of Integer Sequences | S1,S6,S8,S9 | B | strong |
| One half | S1,S5,S6,S8,S9 | Start | strong |
| One in ten rule | S1 | Stub | strong |
| One Through Zero (The Ten Numbers) | S6 | | S6 near |
| One- and two-tailed tests | S2,S8,S9 | B | strong |
| One-class classification | S2 | Stub | strong |
| One-dimensional space | S1,S6,S8 | Start | strong |
| One-dimensional symmetry group | S1,S6,S9 | Start | strong |
| One-factor-at-a-time method | S2 | Stub | strong |
| One-form | S1,S4,S5,S6,S8,S9 | Start | strong |
| One-key MAC | S2,S5,S6 | Start | strong |
| One-parameter group | S1,S4,S6,S8,S9 | Start | strong |
| One-relator group | S1,S4,S6,S9 | C | strong |
| One-seventh area triangle | S1,S6,S8,S9 | Start | strong |
| One-shot deviation principle | S5,S6 | | S6 near |
| One-sided limit | S1,S4,S5,S6,S8,S9 | Start | strong |
| One-step method | S1,S6 | C | strong |
| One-time pad | S2,S4,S5,S6,S8 | C | strong |
| One-time password | S2,S8 | B | strong |
| One-way analysis of variance | S1,S2,S9 | Start | strong |
| One-way compression function | S2,S5,S6 | C | strong |
| One-way function | S1,S2,S4,S5,S6,S8 | Start | strong |
| One-way wave equation | S1,S3 | Start | strong |
| Ones' complement | S1,S3,S5,S6 | Start | strong |
| Online analytical processing | S2,S3 | C | strong |
| Online fair division | S1,S6 | Start | strong |
| Online matrix-vector multiplication problem | S1,S3,S5,S6 | C | strong |
| Onno J. Boxma | S1,S8,S9 | Start | strong |
| Ono's inequality | S1,S5,S6,S8,S9 | Stub | strong |
| Onofrio Puglisi | S1,S8 | Stub | strong |
| Onorato Candiota | S1 | Stub | strong |
| Onorato Nicoletti | S1,S8 | Stub | strong |
| Onsager reciprocal relations | S3,S4,S5,S6,S9 | Start | strong |
| Onsager–Machlup function | S6 | | S6 near |
| Ontological commitment | S2 | Start | strong |
| Ontological maximalism | S1,S2,S6 | Stub | strong |
| Ooguri–Vafa metric | S1,S6 | Stub | strong |
| Oort constants | S3,S4 | C | strong |
| Opacity | S3,S4,S5,S6 | Start | strong |
| Opaque context | S2,S8 | Start | strong |
| Opaque set | S1,S6,S8,S9 | GA | strong |
| Open and closed maps | S1,S4,S5,S6,S8,S9 | C | strong |
| Open book decomposition | S1,S4,S6,S9 | Start | strong |
| Open coloring axiom | S1,S6,S8,S9 | Stub | strong |
| Open formula | S1,S2,S5,S6,S8,S9 | Start | strong |
| Open knot theory | S1,S6,S8,S9 | C | strong |
| Open mapping theorem (complex analysis) | S1,S4,S5,S6,S8,S9 | Start | strong |
| Open mapping theorem (functional analysis) | S1,S4,S5,S6,S8,S9 | Start | strong |
| Open Mathematics | S1,S8 | Start | strong |
| Open problem | S1,S3,S5,S8 | Start | strong |
| Open Problems in Mathematics | S1,S6,S8,S9 | Start | strong |
| Open quantum system | S3,S4,S5 | Start | strong |
| Open set | S1,S4,S5,S6,S8,S9 | C | strong |
| Open set condition | S1,S6 | Start | strong |
| Open Technology Fund | S2 | C | strong |
| Open Web Analytics | S2 | Stub | strong |
| Open Whisper Systems | S2 | B | strong |
| Open-access poll | S2 | Start | strong |
| Open-label trial | S2 | Stub | strong |
| Open-loop model | S6 | | S6 near |
| Open-question argument | S2 | C | strong |
| OpenBSD Cryptographic Framework | S2,S6 | Start | strong |
| OpenBUGS | S2,S9 | Start | strong |
| OpenEpi | S2,S6 | C | strong |
| OpenIntro Statistics | S2 | Stub | strong |
| OpenMath | S1,S6,S9 | Start | strong |
| OpenMx | S2 | Start | strong |
| OpenPGP card | S2 | | strong |
| OpenSSH | S2 | B | strong |
| OpenSSL | S2 | B | strong |
| OpenVPN | S2 | C | strong |
| Oper (mathematics) | S1,S3,S6 | Start | strong |
| Operad | S1,S4,S5,S6,S8,S9 | C | strong |
| Operad algebra | S1,S4,S5,S6,S9 | Stub | strong |
| Operand | S1,S5,S6,S9 | C | strong |
| Operation (mathematics) | S1,S4,S5,S6,S8,S9 | Start | strong |
| Operation Rubicon | S2 | C | strong |
| Operational analytical processing | S2 | Start | strong |
| Operational calculus | S1,S4,S5,S6,S9 | C | strong |
| Operational semantics | S3,S4,S5,S6,S9 | Start | strong |
| Operational sex ratio | S2 | Start | strong |
| Operationalization | S2 | Start | strong |
| Operations research | S1,S2,S3,S4,S5,S6,S8,S9 | C | strong |
| Operations Support Branch | S2 | Start | strong |
| Operator (mathematics) | S1,S4,S5,S6,S8,S9 | C | strong |
| Operator algebra | S1,S5,S6,S8,S9 | Start | strong |
| Operator ideal | S1,S6,S9 | Stub | strong |
| Operator K-theory | S1,S4,S5,S6,S8,S9 | Stub | strong |
| Operator monotone function | S1,S4,S6,S9 | Stub | strong |
| Operator norm | S1,S4,S5,S6,S8,S9 | C | strong |
| Operator product expansion | S3,S4,S5,S9 | Start | strong |
| Operator space | S1,S4,S5,S6,S8,S9 | Start | strong |
| Operator system | S1,S4,S6,S9 | Stub | strong |
| Operator theory | S1,S4,S5,S6,S8,S9 | C | strong |
| Operator topologies | S1,S5,S6,S8,S9 | Start | strong |
| Opetope | S1,S5,S6,S8,S9 | Stub | strong |
| Opial property | S1 | Start | strong |
| Opinion | S2,S8 | Start | strong |
| Opinion poll | S2,S8,S9 | C | strong |
| Opinion polling and analysis about Islamic fundamentalism | S2 | Start | strong |
| Opinion polling for the 1966 United Kingdom general election | S2 | Start | strong |
| Opinion polling for the 2009 Greek parliamentary election | S2 | List | strong |
| Opinion polling for the 2017 South Korean presidential election | S2 | List | strong |
| Opinion polling for the 2018 Mexican general election | S2 | List | strong |
| Opinion polling for the 2019 Greek parliamentary election | S2 | List | strong |
| Opinion polling for the 2019 Indian general election | S2 | C | strong |
| Opinion polling for the 2022 Israeli legislative election | S2 | Start | strong |
| Opinion polling for the 2023 Dutch general election | S2 | List | strong |
| Opinion polling for the 2024 Indian general election | S2 | B | strong |
| Opinion polling for the 2025 Dutch general election | S2 | List | strong |
| Opinion polling for the 2026 Israeli legislative election | S2 | List | strong |
| Opinion polling for the 2026 Portuguese presidential election | S2 | List | strong |
| Opinion polling for the 2029 Indonesian presidential election | S2 | | strong |
| Opinion polling for the May 2023 Greek parliamentary election | S2 | List | strong |
| Opinion polling for the next South Korean legislative election | S2 | C | strong |
| Opinion polls in Venezuela | S2 | C | strong |
| Oppenheim conjecture | S1,S4,S5,S6,S8,S9 | Start | strong |
| Oppenheimer–Snyder model | S3,S4,S8 | C | strong |
| Oppermann's conjecture | S1,S5,S6,S8,S9 | Start | strong |
| Opportunistic encryption | S2 | C | strong |
| Opportunistic TLS | S2 | Start | strong |
| Opportunistic Wireless Encryption | S2 | Start | strong |
| Opposite category | S1,S4,S5,S6,S8,S9 | Start | strong |
| Opposite group | S1,S4,S6,S9 | Start | strong |
| Opposite ring | S1,S4,S6,S8,S9 | Start | strong |
| Opposite simplicial set | S1,S6 | | strong |
| Optic equation | S1,S6,S9 | C | strong |
| Optical aberration | S3,S4,S6 | C | strong |
| Optical depth | S3,S4 | Start | strong |
| Optical fiber | S3,S4,S8 | C | strong |
| Optical parametric amplifier | S3,S4 | Start | strong |
| Optical path length | S3,S4,S5,S6 | Start | strong |
| Optical rotation | S3,S4,S6 | C | strong |
| Optical space | S6 | | S6 near |
| Optical theorem | S3,S4,S5,S8 | Start | strong |
| Optical transfer function | S3,S4,S5 | C | strong |
| Optical vortex | S3,S4,S6 | Start | strong |
| OPTICS algorithm | S2,S5,S9 | C | strong |
| Optimal apportionment | S1,S6 | Start | strong |
| Optimal asymmetric encryption padding | S2 | Start | strong |
| Optimal control | S1,S3,S4,S6,S8,S9 | C | strong |
| Optimal decision | S1,S2,S8 | Start | strong |
| Optimal discriminant analysis and classification tree analysis | S2 | Stub | strong |
| Optimal estimation | S1,S6 | Start | strong |
| Optimal experimental design | S1,S2,S4,S6,S8,S9 | C | strong |
| Optimal facility location | S1,S3,S4,S5,S6,S8,S9 | Start | strong |
| Optimal instruments | S2,S6 | Start | strong |
| Optimal job scheduling | S3,S4 | | strong |
| Optimal matching | S1,S2,S6,S9 | Start | strong |
| Optimal radix choice | S1,S5,S6,S8 | C | strong |
| Optimal solutions for the Rubik's Cube | S6,S8 | | S6 near |
| Optimal stable matching | S1,S2,S6 | C | strong |
| Optimal stopping | S1,S2,S4,S5,S6,S8,S9 | C | strong |
| Optimality criterion | S2 | Stub | strong |
| Optimism bias | S2 | B | strong |
| Optimistic knowledge gradient | S2,S6 | Start | strong |
| Optimization problem | S3,S4,S6,S8 | Stub | strong |
| Optimization Programming Language | S1,S3 | Stub | strong |
| Optional stopping theorem | S1,S2,S4,S5,S6,S8,S9 | Start | strong |
| Oracle attack | S1 | Stub | strong |
| Oracle complexity (optimization) | S1,S6 | Start | strong |
| Oracle machine | S1,S3,S4,S6,S8 | C | strong |
| Orazio Grassi | S1,S8,S9 | C | strong |
| Orbifold | S1,S4,S5,S6,S8,S9 | B | strong |
| Orbifold notation | S1,S5,S6,S8,S9 | Start | strong |
| Orbit (dynamics) | S3,S4,S6,S9 | Start | strong |
| Orbit capacity | S1,S6 | Start | strong |
| Orbit method | S1,S4,S5,S8 | C | strong |
| Orbit modeling | S3,S6 | C | S6 near |
| Orbit portrait | S1,S3,S5,S6,S9 | Start | strong |
| Orbit trap | S1,S6,S9 | Start | strong |
| Orbital angular momentum of light | S3,S4,S6 | C | strong |
| Orbital elements | S3,S4,S8 | C | strong |
| Orbital integral | S1,S3,S6,S9 | Start | strong |
| Orbital mechanics | S3,S4,S5,S8 | B | strong |
| Orbital node | S3,S6,S9 | Start | S6 near |
| Orbital overlap | S6,S9 | | S6 near |
| Orbital plane | S3,S6,S8 | Start | S6 near |
| Orbital plane of reference | S3,S6 | Stub | S6 near |
| Orbital resonance | S4 | | strong |
| Orbital stability | S1,S3,S5,S6 | Start | strong |
| Orbot | S2 | Start | strong |
| Orchard-planting problem | S1,S4,S5,S6,S8,S9 | Start | strong |
| Order (group theory) | S1,S4,S5,S6,S8,S9 | Start | strong |
| Order (journal) | S1,S6,S8,S9 | Stub | strong |
| Order (mathematics) | S1,S6,S9 | List | strong |
| Order (ring theory) | S1,S4,S6,S8,S9 | Start | strong |
| Order bound dual | S1,S6,S9 | Start | strong |
| Order complete | S1,S6,S9 | Stub | strong |
| Order convergence | S1,S6,S9 | Start | strong |
| Order dimension | S1,S4,S5,S6 | Start | strong |
| Order dual (functional analysis) | S1,S6,S9 | Start | strong |
| Order embedding | S1,S4,S6,S8 | Start | strong |
| Order isomorphism | S1,S4,S6,S8 | Start | strong |
| Order of a kernel | S1,S2 | Stub | strong |
| Order of accuracy | S1,S6,S8,S9 | Stub | strong |
| Order of approximation | S1,S2,S6,S8,S9 | C | strong |
| Order of integration | S2 | Start | strong |
| Order of integration (calculus) | S1,S4,S6,S8,S9 | C | strong |
| Order of magnitude | S1,S5,S6,S8,S9 | C | strong |
| Order of operations | S1,S3,S5,S6,S8,S9 | B | strong |
| Order polynomial | S1,S4,S6,S9 | Start | strong |
| Order polytope | S1,S4,S6,S9 | C | strong |
| Order statistic | S2,S4,S5,S6,S8,S9 | C | strong |
| Order summable | S1,S6,S9 | Stub | strong |
| Order theory | S1,S4,S5,S6,S8 | C | strong |
| Order topology | S1,S4,S5,S6,S8,S9 | Start | strong |
| Order topology (functional analysis) | S1,S6,S8,S9 | Start | strong |
| Order type | S1,S4,S5,S6,S8,S9 | Start | strong |
| Order unit | S1,S6,S9 | Stub | strong |
| Order-2 apeirogonal tiling | S1,S6,S8,S9 | Stub | strong |
| Order-3 apeirogonal tiling | S1,S6,S8 | Start | strong |
| Order-3-7 hexagonal honeycomb | S1,S8 | Start | strong |
| Order-4 120-cell honeycomb | S1,S6,S8,S9 | Stub | strong |
| Order-4 24-cell honeycomb | S1,S6,S8,S9 | Stub | strong |
| Order-4 24-cell honeycomb honeycomb | S1,S6,S8 | Stub | strong |
| Order-4 apeirogonal tiling | S1,S6,S8 | Stub | strong |
| Order-4 dodecahedral honeycomb | S1,S8 | Stub | strong |
| Order-4 heptagonal tiling | S1,S6,S8,S9 | Stub | strong |
| Order-4 hexagonal tiling | S1,S6,S8 | Start | strong |
| Order-4 hexagonal tiling honeycomb | S1,S8 | Start | strong |
| Order-4 octagonal tiling | S1,S6,S8 | C | strong |
| Order-4 octahedral honeycomb | S1,S8 | Start | strong |
| Order-4 pentagonal tiling | S1,S5,S6,S8,S9 | Stub | strong |
| Order-4 square tiling honeycomb | S1,S6,S8 | Start | strong |
| Order-5 120-cell honeycomb | S1,S6,S8,S9 | Stub | strong |
| Order-5 5-cell honeycomb | S1,S6,S8,S9 | Stub | strong |
| Order-5 apeirogonal tiling | S1,S6,S8 | Stub | strong |
| Order-5 cubic honeycomb | S1,S8 | Stub | strong |
| Order-5 dodecahedral honeycomb | S1,S6,S8 | Stub | strong |
| Order-5 hexagonal tiling honeycomb | S1,S8 | Start | strong |
| Order-5 icosahedral 120-cell honeycomb | S1,S5,S6,S8,S9 | Stub | strong |
| Order-5 octahedral honeycomb | S1,S8 | C | strong |
| Order-5 pentagonal tiling | S1,S6,S8,S9 | Stub | strong |
| Order-5 square tiling | S1,S5,S6,S8,S9 | Stub | strong |
| Order-5 tesseractic honeycomb | S1,S8 | Stub | strong |
| Order-5 truncated pentagonal hexecontahedron | S1,S6 | Stub | strong |
| Order-6 apeirogonal tiling | S1,S6,S8 | Start | strong |
| Order-6 dodecahedral honeycomb | S1,S8 | Start | strong |
| Order-6 hexagonal tiling | S1,S6,S8 | Start | strong |
| Order-6 hexagonal tiling honeycomb | S1,S6,S8 | Start | strong |
| Order-6 pentagonal tiling | S1,S6,S8 | Stub | strong |
| Order-6 square tiling | S1,S6,S8 | Start | strong |
| Order-6 tetrahedral honeycomb | S1,S5,S8 | Start | strong |
| Order-7 dodecahedral honeycomb | S1,S8 | Start | strong |
| Order-7 heptagrammic tiling | S1,S6,S8,S9 | Stub | strong |
| Order-7 tetrahedral honeycomb | S1,S5,S8 | Stub | strong |
| Order-7 triangular tiling | S1,S6,S8 | Start | strong |
| Order-8 triangular tiling | S1,S6,S8 | C | strong |
| Ordered algebra | S1,S6 | Stub | strong |
| Ordered Bell number | S1,S5,S6,S9 | GA | strong |
| Ordered exponential field | S1,S6,S8,S9 | Start | strong |
| Ordered field | S1,S4,S5,S6,S8,S9 | Start | strong |
| Ordered geometry | S1,S4,S5,S6,S8,S9 | Start | strong |
| Ordered graph | S1,S6 | Start | strong |
| Ordered logit | S1,S2 | Start | strong |
| Ordered pair | S1,S4,S5,S6,S8,S9 | C | strong |
| Ordered ring | S1,S4,S6,S8,S9 | C | strong |
| Ordered semigroup | S1,S4,S5,S6,S9 | Stub | strong |
| Ordered set operators | S1,S5,S6 | List | strong |
| Ordered subset expectation maximization | S1,S2,S6,S8 | Stub | strong |
| Ordered topological vector space | S1,S6,S8,S9 | Start | strong |
| Ordered vector space | S1,S4,S6,S8,S9 | Start | strong |
| Ordered weighted averaging | S1,S3,S6 | Start | strong |
| Orders of magnitude (area) | S1 | Start | strong |
| Orders of magnitude (entropy) | S2,S3,S6 | List | strong |
| Orders of magnitude (length) | S1,S3 | List | strong |
| Orders of magnitude (numbers) | S1,S5,S8 | List | strong |
| Orders of magnitude (probability) | S2,S6,S9 | List | strong |
| Orders of magnitude (volume) | S1 | List | strong |
| Ordinal analysis | S1,S4,S5,S6,S8,S9 | Start | strong |
| Ordinal arithmetic | S1,S4,S5,S6,S8,S9 | B | strong |
| Ordinal collapsing function | S1,S6,S9 | C | strong |
| Ordinal data | S1,S2,S6,S9 | Start | strong |
| Ordinal definable set | S1,S5,S6,S8,S9 | Stub | strong |
| Ordinal logic | S1,S6 | Stub | strong |
| Ordinal notation | S1,S6,S9 | Start | strong |
| Ordinal number | S1,S4,S5,S6,S8,S9 | B | strong |
| Ordinal regression | S2 | Start | strong |
| Ordinary differential equation | S1,S4,S5,S6,S8,S9 | B | strong |
| Ordinary Differential Equations (textbook) | S1 | Stub | strong |
| Ordinary least squares | S1,S2,S4,S5,S8,S9 | B | strong |
| Ordinary singularity | S1,S6 | Stub | strong |
| Ordination (statistics) | S2 | Stub | strong |
| Ore | S4 | | strong |
| Ore algebra | S1,S5,S6,S9 | Stub | strong |
| Ore condition | S1,S4,S5,S6,S8,S9 | Start | strong |
| Ore extension | S1,S4,S5,S6,S9 | Start | strong |
| Ore's theorem | S1,S5,S6,S8,S9 | Start | strong |
| Oregonator | S4,S6,S8 | | strong |
| Oren Patashnik | S1,S3,S8 | Stub | strong |
| Organon | S2,S6,S8,S9 | C | strong |
| Orientability | S1,S4,S5,S6,S8,S9 | C | strong |
| Orientation (geometry) | S1,S6,S8,S9 | C | strong |
| Orientation (graph theory) | S1,S5,S6,S8,S9 | Start | strong |
| Orientation (vector space) | S1,S4,S5,S6,S9 | C | strong |
| Orientation character | S1,S6,S8,S9 | Stub | strong |
| Orientation entanglement | S1,S3,S6,S9 | Start | strong |
| Orientation of a vector bundle | S1,S5,S6,S8,S9 | Start | strong |
| Orientation sheaf | S1,S6,S8,S9 | Stub | strong |
| Oriented coloring | S1,S6 | Start | strong |
| Oriented matroid | S1,S3,S4,S5,S6 | C | strong |
| Oriented projective geometry | S1,S3 | Start | strong |
| Origami Polyhedra Design | S1,S6,S8,S9 | Start | strong |
| Origamics | S1,S6,S9 | Start | strong |
| Origin (data analysis software) | S2,S9 | C | strong |
| Origin (mathematics) | S1,S5,S6,S8,S9 | Start | strong |
| Original proof of Gödel's completeness theorem | S1,S2,S5,S6,S8,S9 | Start | strong |
| Orlicz sequence space | S1,S5,S6,S9 | Start | strong |
| Orlicz space | S1,S4,S5,S6,S8,S9 | Start | strong |
| Orlicz–Pettis theorem | S1,S4,S5,S6,S8,S9 | Stub | strong |
| Ornstein isomorphism theorem | S1,S4,S5,S6,S8 | Start | strong |
| Ornstein–Uhlenbeck operator | S1,S5,S6 | C | strong |
| Ornstein–Uhlenbeck process | S1,S2,S4,S5,S8,S9 | Start | strong |
| Ornstein–Zernike equation | S3,S4,S5,S6 | Start | strong |
| Orrin Frink | S1,S8,S9 | Start | strong |
| Orr–Sommerfeld equation | S3,S4,S5,S8 | C | strong |
| Orthant | S1,S5,S6,S9 | Start | strong |
| Orthocenter | S1,S4,S5,S8 | C | strong |
| Orthocentric system | S1,S4,S5,S6,S8,S9 | Start | strong |
| Orthocentric tetrahedron | S1 | Start | strong |
| Orthocentroidal circle | S1,S5,S8 | Start | strong |
| Orthocompact space | S1,S6,S8,S9 | Stub | strong |
| Orthodiagonal quadrilateral | S1,S5,S8 | Start | strong |
| Orthodox semigroup | S1,S6,S9 | Start | strong |
| Orthogonal array | S1,S2,S6,S8,S9 | B | strong |
| Orthogonal array testing | S2 | Start | strong |
| Orthogonal basis | S1,S5,S6,S9 | Start | strong |
| Orthogonal circles | S1,S6,S9 | Stub | strong |
| Orthogonal complement | S1,S4,S6,S8,S9 | C | strong |
| Orthogonal convex hull | S1,S3,S6,S8 | C | strong |
| Orthogonal coordinates | S1,S5,S6 | C | strong |
| Orthogonal diagonalization | S1,S6,S9 | Stub | strong |
| Orthogonal functions | S1,S5,S6,S8,S9 | Start | strong |
| Orthogonal group | S1,S4,S5,S6,S8,S9 | B | strong |
| Orthogonal matrix | S1,S4,S5,S6,S8,S9 | B | strong |
| Orthogonal polyhedron | S1,S6,S9 | Start | strong |
| Orthogonal polynomials | S1,S4,S5,S6,S8 | B | strong |
| Orthogonal polynomials on the unit circle | S1,S4,S6,S8 | Start | strong |
| Orthogonal Procrustes problem | S1,S6,S9 | Start | strong |
| Orthogonal signal correction | S2,S6 | Stub | strong |
| Orthogonal symmetric Lie algebra | S1,S9 | Stub | strong |
| Orthogonal trajectory | S1,S5 | Stub | strong |
| Orthogonal transformation | S1,S5,S6,S9 | Start | strong |
| Orthogonal wavelet | S1 | Start | strong |
| Orthogonality | S1,S2,S5,S6,S8 | B | strong |
| Orthogonality (mathematics) | S1,S4,S6,S8,S9 | C | strong |
| Orthogonality principle | S2 | C | strong |
| Orthogonalization | S1,S5,S6,S8,S9 | Start | strong |
| Orthographic projection | S1,S3,S5,S6,S8,S9 | C | strong |
| Orthologic triangles | S1,S5,S6,S9 | Start | strong |
| Orthomorphism | S1,S5,S6 | Stub | strong |
| Orthonormal basis | S1,S4,S5,S6,S8,S9 | C | strong |
| Orthonormal frame | S1,S5,S9 | Stub | strong |
| Orthonormal function system | S1,S5,S6 | Stub | strong |
| Orthonormality | S1,S4,S5,S6,S8,S9 | C | strong |
| Orthopole | S1,S5,S6,S8 | Stub | strong |
| Orthoptic (geometry) | S1,S5,S8 | C | strong |
| Orthorhombic crystal system | S1,S3,S5 | Start | strong |
| Orthostochastic matrix | S1,S2,S6 | Stub | strong |
| Orthotropic material | S3,S4,S6,S9 | B | strong |
| Orymbek Zhautykov | S1 | C | strong |
| Oscar Bruno | S1,S8 | Start | strong |
| Oscar Chisini | S1,S8,S9 | Stub | strong |
| Oscar Goldman (mathematician) | S1,S9 | Stub | strong |
| Oscar Kempthorne | S1,S2,S8,S9 | Start | strong |
| Oscar Randal-Williams | S1,S5,S8,S9 | Stub | strong |
| Oscar S. Adams | S1,S9 | C | strong |
| Oscar Zariski | S1,S4,S8,S9 | C | strong |
| Oscillation (mathematics) | S1,S4,S5,S6,S8,S9 | Start | strong |
| Oscillation theory | S1,S4,S8,S9 | Start | strong |
| Oscillator representation | S1,S4,S5,S6,S8,S9 | C | strong |
| Oscillatory integral | S1,S4,S5,S6,S8,S9 | Start | strong |
| Oscillatory integral operator | S1,S6,S8,S9 | Start | strong |
| Osculant | S1,S6,S8 | Stub | strong |
| Osculating circle | S1,S4,S5,S6,S8,S9 | Start | strong |
| Osculating curve | S1,S5 | Start | strong |
| Osculating orbit | S3,S4 | Start | strong |
| Osculating plane | S1,S5,S6,S8,S9 | Start | strong |
| Oseen equations | S3,S4,S5 | Start | strong |
| Oseledets theorem | S1,S3,S4,S5,S6,S8,S9 | Start | strong |
| Osgood curve | S1,S5,S8 | Start | strong |
| Osgood's lemma | S1,S5,S6,S9 | Stub | strong |
| Oskar Anderson | S2,S5,S8,S9 | Start | strong |
| Oskar Becker | S2,S8 | Start | strong |
| Oskar Bolza | S1,S8,S9 | C | strong |
| Oskar Perron | S1,S5,S8,S9 | Stub | strong |
| Oskar Schlömilch | S1,S8,S9 | Stub | strong |
| Osmo Pekonen | S1,S9 | Stub | strong |
| Osserman manifold | S1,S6,S8,S9 | Stub | strong |
| Osserman–Xavier–Fujimoto theorem | S1,S5,S6 | Stub | strong |
| Ostilio Ricci | S1,S8 | Start | strong |
| Ostomachion | S1,S5,S6,S8,S9 | Start | strong |
| Ostrogradsky instability | S1,S5,S6 | Start | strong |
| Ostrowski | S4 | | strong |
| Ostrowski numeration | S1,S5 | Start | strong |
| Ostrowski Prize | S1,S9 | Start | strong |
| Ostrowski's theorem | S1,S5,S6,S8,S9 | Start | strong |
| Ostwald ripening | S3,S4 | Start | strong |
| Oswald Leroy | S1 | C | strong |
| Oswald Veblen Prize in Geometry | S6,S8,S9 | | S6 near |
| Oswaldo Castro | S2 | C | strong |
| Oswaldo Lezama | S1 | Start | strong |
| Otakar Borůvka | S1,S9 | Start | strong |
| Otfrid Mittmann | S1,S8,S9 | Stub | strong |
| Otomar Hájek | S1,S9 | Stub | strong |
| Ott-Heinrich Keller | S1,S9 | Start | strong |
| Ottaviano Menni | S1 | Stub | strong |
| Ottavio Scarlattini | S1 | Stub | strong |
| Otto calculus | S1,S6 | Stub | strong |
| Otto cycle | S3,S4 | C | strong |
| Otto Dersch | S1,S8 | Stub | strong |
| Otto E. Neugebauer | S1,S8,S9 | Start | strong |
| Otto Forster | S1,S8,S9 | Start | strong |
| Otto Frostman | S1,S8,S9 | Stub | strong |
| Otto Grün | S1 | Stub | strong |
| Otto H. Kegel | S1,S9 | Start | strong |
| Otto Haupt | S1,S9 | Stub | strong |
| Otto Hesse | S1,S8,S9 | Stub | strong |
| Otto Hölder | S1,S8,S9 | Start | strong |
| Otto Leiberich | S1,S9 | Start | strong |
| Otto M. Nikodym | S1,S5,S8,S9 | Stub | strong |
| Otto Schilling | S1,S8,S9 | Stub | strong |
| Otto Schreier | S1,S5,S6,S8,S9 | Start | strong |
| Otto Toeplitz | S1,S6,S8,S9 | C | strong |
| Otto Weininger | S2 | C | strong |
| Otway–Rees protocol | S2,S6 | Stub | strong |
| Oum Sang-il | S1,S9 | C | strong |
| Ouroboros (protocol) | S2 | Start | strong |
| Out(Fn) | S1,S4,S6,S9 | Start | strong |
| Out-of-bag error | S2,S3,S6 | C | strong |
| Outcome (game theory) | S6 | | S6 near |
| Outcome (probability) | S1,S2,S4,S5,S9 | Start | strong |
| Outcome switching | S2,S6 | C | strong |
| Outer automorphism group | S1,S4,S5,S6,S8,S9 | Start | strong |
| Outer measure | S1,S4,S5,S6,S8 | Start | strong |
| Outer product | S1,S5,S8,S9 | B | strong |
| Outer space (mathematics) | S1,S5,S6,S9 | C | strong |
| Outermorphism | S1,S6 | Start | strong |
| Outerplanar graph | S1,S5,S6,S8 | C | strong |
| Outlier | S2,S5,S8,S9 | B | strong |
| Outliers ratio | S2,S6 | Stub | strong |
| Outline of actuarial science | S1,S2,S6 | List | strong |
| Outline of algebra | S1,S6,S8,S9 | List | strong |
| Outline of algebraic structures | S6,S8,S9 | | S6 near |
| Outline of arithmetic | S6,S8 | | S6 near |
| Outline of calculus | S6,S8,S9 | | S6 near |
| Outline of category theory | S6,S8,S9 | | S6 near |
| Outline of combinatorics | S6,S8 | | S6 near |
| Outline of cryptography | S2,S6 | List | strong |
| Outline of discrete mathematics | S1,S6,S8,S9 | List | strong |
| Outline of geometry | S1,S6,S8,S9 | | strong |
| Outline of Gottfried Wilhelm Leibniz | S6,S9 | | S6 near |
| Outline of linear algebra | S1,S6,S8,S9 | List | strong |
| Outline of logic | S1,S2,S6,S8,S9 | List | strong |
| Outline of probability | S1,S2,S6,S8,S9 | List | strong |
| Outline of regression analysis | S2,S6,S8,S9 | List | strong |
| Outline of statistics | S1,S2,S6,S8,S9 | List | strong |
| Outline of trigonometry | S1,S6,S8,S9 | List | strong |
| Outline of vector identities | S1,S6,S8 | Stub | strong |
| Oval | S1,S5,S6,S8 | Start | strong |
| Oval (projective plane) | S1,S4,S6,S8,S9 | Start | strong |
| Overcategory | S1,S6,S8,S9 | Start | strong |
| Overcompleteness | S1,S6,S8,S9 | Start | strong |
| Overconfidence effect | S2 | C | strong |
| Overconvergent modular form | S1,S6 | Stub | strong |
| Overdetermined system | S1,S4,S6,S9 | Start | strong |
| Overdispersion | S2,S6,S9 | Start | strong |
| Overfitting | S2,S6,S9 | C | strong |
| Overfull graph | S1,S5,S6,S8 | Start | strong |
| Overlap (term rewriting) | S1,S5,S6 | Stub | strong |
| Overlapping circles grid | S1,S5,S6,S8,S9 | C | strong |
| Overlapping generations model | S4 | | strong |
| Overlapping interval topology | S1,S6,S8,S9 | Stub | strong |
| Overline | S1,S5,S8 | C | strong |
| Overring | S1,S6,S9 | Stub | strong |
| Oversampling and undersampling in data analysis | S2 | Start | strong |
| Overshoot (signal) | S1,S3,S6 | C | strong |
| Overspill | S1,S5,S6,S8,S9 | Start | strong |
| Overview of news media phone hacking scandals | S2 | B | strong |
| Overwhelming exception | S2,S9 | Stub | strong |
| Ovidiu Savin | S1,S8,S9 | Start | strong |
| Ovoid (polar space) | S1,S6 | Start | strong |
| Ovoid (projective geometry) | S1,S4,S6,S9 | C | strong |
| Owen's T function | S2,S5,S6,S8 | Stub | strong |
| Oxford Bulletin of Economics and Statistics | S2 | Start | strong |
| Oxford Calculators | S2,S3 | C | strong |
| Oxford University Invariant Society | S1,S9 | Start | strong |
| OxMetrics | S2,S9 | Start | strong |