An **edge** is (together with vertices) one of the two basic units out of which graphs are constructed. Each **edge** has two (or in hypergraphs, more) vertices to which it is attached, called its endpoints.

**Edges** may be:

- undirected edges (also called lines)
- directed edges (also called arcs or arrows)

In an undirected simple graph, an edge may be represented as the set of its vertices, and in a directed simple graph it may be represented as an ordered pair of its vertices.

An **edge** that connects vertices