A sigma-algebra which is related to the topology of a set. The Borel -algebra is defined to be the sigma-algebra generated by the open sets (or equivalently, by the closed sets).
Borel Sigma-Algebra
See also
Borel Measure, Sigma-AlgebraExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Borel Sigma-Algebra." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/BorelSigma-Algebra.html