Definition:Interior Point (Topology)/Definition 2

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

Let $H \subseteq S$.

Let $h \in H$.

$h$ is an interior point of $H$ iff $h$ has an open neighborhood $N_h$ such that $N_h \subseteq H$.

Also see

 * Equivalence of Definitions of Interior Point