\begin{definition}[Definition:Interior Point (Complex Analysis)]
Let $S \subseteq \C$ be a subset of the complex plane.
Let $z \in S$.
$z$ is an '''interior point''' of $S$ {{iff}} $z$ has an $\epsilon$-neighborhood $\map {N_\epsilon} z$ such that $\map {N_\epsilon} z \subseteq S$.
\end{definition}