Countably generated space

A **countably generated space** is a type of topological space that can be described in terms of its open sets. Specifically, a topological space \( X \) is called countably generated if there exists a countable collection of open sets \( \{ U_n \}_{n=1}^\infty \) such that the smallest topology on \( X \) generated by these open sets is the same as the original topology on \( X \).