Definition:Accumulation Point/Set

Definition
Let $\paren { S, \tau }$ be a topological space.

Let $A \subseteq S$. Let $x \in S$.

Then $x$ is an accumulation point of $A$ :
 * $x \in \cl {A \setminus \set x}$

where $\operatorname{cl}$ denotes the (topological) closure of a set.