# Math Insight

### Edge definition

An edge (or link) of a network (or graph) is one of the connections between the nodes (or vertices) of the network. Edges can be directed, meaning they point from one node to the next, as illustrated by the arrows in the first figure below. Edges can also be undirected, in which case they are bidirectional, as illustrated by the lines in the second figure, below.

A directed network with 10 nodes (or vertices) and 13 edges (or links).

An undirected network with 10 nodes (or vertices) and 11 edges (or links).