 CW complex

A CW complex is built inductively by attaching discs along maps from their boundary spheres. Its $n$-skeleton contains all cells of dimension at most $n$.

A CW complex (pronounced "C-W complex") is a type of topological space that is particularly useful in algebraic topology. The term "CW" stands for "cellular" and "weak," referring to the construction method used to create such complexes. A CW complex is constructed using "cells," which are basic building blocks, typically in the shape of disks of different dimensions.