P-space

Definition
A topological space is termed a P-space if every $$G_\delta$$-subset in it is open.

Formalisms
The property of being a P-space can be described as the following implication between properties of subsets:

$$G_\delta \implies$$ Open

Stronger properties

 * Alexandroff space

Weaker properties

 * P'-space
 * Countably orthocompact space