Definition:Adjacent (Graph Theory)/Edges/Digraph

Definition
Let $G = \left({V, E}\right)$ be a digraph.

Two arcs $e_1, e_2 \in E$ of $G$ adjacent if there exists a vertex $v \in V$ to which they are both incident.

Otherwise they are non-adjacent.

Also known as
Adjacent arcs can also be described as neighboring (British English spelling: neighbouring).