Atom

Summary

In a partially ordered set with a least element $0$, an atom is an element just above $0$. It is above $0$, and nothing lies strictly between $0$ and it. Atoms are the minimal nonzero elements. In the lattice of subsets of a set they are the one-element subsets, which is the origin of the name. Atoms are used to define atomic and atomistic lattices and to describe Boolean algebras.