Second-countable space

In topology, a **second-countable space** is a type of topological space that has a specific property related to its basis. A topological space \(X\) is said to be second-countable if it has a countable basis for its topology. More formally, a **basis** for a topology on a set \(X\) is a collection of open sets such that every open set in the topology can be expressed as a union of sets from this basis.