Definition:Separated by Neighborhoods/Sets/Open Sets

Definition
Let $T = \left({S, \tau}\right)$ be a topological space.

Let $A, B \subseteq S$ such that:
 * $\exists U, V \in \tau: A \subseteq U, B \subseteq V: U \cap V = \varnothing$

That is, that $A$ and $B$ both have open neighborhoods in $T$ which are disjoint.

Then $A$ and $B$ are described as separated by (open) neighborhoods.