Definition:Open Cover

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

Let $\mathcal C$ be a cover for $S$.

Then $\mathcal C$ is an open cover :
 * $\mathcal C \subseteq \tau$

That is, all the elements of $\mathcal C$ are open sets.

Also known as
Some sources have this as open covering.