Dowker space

In topology, a **Dowker space** is a specific kind of topological space that has peculiar properties related to separability. A space \(X\) is called a Dowker space if it is a normal space (which means that any two disjoint closed sets can be separated by neighborhoods) but not every countable closed set in \(X\) can be separated from a point not in the closed set by disjoint neighborhoods.