A digraph (or directed graph) consists of a number of vertices, some of which are joined by arcs, where an arc, or directed edge or arrow, joins one vertex to another and has an arrow on it to indicate its direction. The arc from the vertex u to the vertex v may be denoted by the ordered pair (u, v). The digraph with vertices u, v, w, x and arcs (u, v), (u, w), (v, u), (w, v), (w, x) is shown in the first figure.

directed graph

directed multigraph

As with graphs there may be multiple arcs and loops, as shown in the second figure.