\begin{definition}[Definition:Adherent Point/Definition 1]
Let $T = \struct {S, \tau}$ be a topological space.
Let $H \subseteq S$.
A point $x \in S$ is an '''adherent point of $H$''' {{iff}} every open neighborhood $U$ of $x$ satisfies:
:$H \cap U \ne \O$
\end{definition}