A directed edge from a graph vertex 
to a graph vertex 
is the ordered pair 
, commonly denoted 
. The vertex 
is its initial vertex and 
is its terminal vertex. A directed edge is also called a graph arc (Jones and Singerman 1978).
In the Wolfram Language, a directed edge is represented by DirectedEdge[u, v]. Inside a graph constructor, the rule u -> v is converted to the same form.
The term bidirected edge may denote a pair of oppositely directed edges or, in a different convention, a single edge with independently directed ends.
