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 and is sometimes written .