---
tag: 0SV8K0TDGY
kind: concept
name: Sigma-algebra
aliases: [sigma-field]
msc: [28A05]
sources:
  - url: https://en.wikipedia.org/wiki/Σ-algebra
    locator: lead section
same_as:
  wikidata: Q217357
  wikipedia: Σ-algebra
---

## Summary

A σ-algebra on a set is a family of subsets that contains the whole set and is closed under complements and countable unions.
In probability theory, the σ-algebra is the family of events, the sets to which we give a probability. The node [[sigma-algebra|04WSW8T3SY]] gives the precise definition.