Definition:Closed Set/Real Analysis/Real Euclidean Space

Definition
Let $n\geq1$ be a natural number.

Let $S \subseteq \R^n$ be a subset.

Then $S$ is closed (in $\R^n$) its complement $\R^n \setminus S$ is an open set.

Also see

 * Definition:Open Subset of Real Euclidean Space
 * Definition:Neighborhood in Real Euclidean Space