Definition:Adjacent (Graph Theory)/Vertices/Digraph

Definition
Let $G = \struct {V, E}$ be a digraph.

Two vertices $u, v \in V$ of $G$ are adjacent there exists an arc $e = \tuple {u, v} \in E$ of $G$ to which they are both incident.

Otherwise they are non-adjacent.

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