independent set and independence number

A set of vertices in a graph $G$ is called an independent set if there are no edges between the vertices.

The independence number of a graph $G$, usually denoted by $\alpha (G)$, is the size of a maximal independent set in $G$. $\alpha (G)\ge \nu$ means that there are $\nu$ vertices with no edges between them.

An independent set is sometimes called a stable set or an anticlique.