graph link

For an undirected graph, an unordered pair of nodes that specify a line joining these two nodes are said to form an edge. For a directed graph, the edge is an ordered pair of nodes. The terms "arc, " "branch, " "line, " "link, " and "1-simplex" are sometimes used instead of edge (e.g., Skiena 1990, p. 80; Harary 1994). Harary calls an edge of a graph a "line." The following table lists the total number of edges in all graphs of given classes on n nodes.

edge count | graph vertex | hyperedge | null graph | Tait coloring | Tait cycle