Definition:Loop (Graph Theory)

Definition
Let $G = \struct {V, E}$ be a loop-graph.

A loop is an edge $e$ of $G$ whose endvertices are the same vertex.

Thus a loop $e$ on the vertex $v$ would be written:
 * $e = vv$

Also known as
Some authors refer to such an edge $e = vv$ as a self-loop at vertex $v$.