Definition:Adjacent (Graph Theory)/Vertices/Digraph

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

Two vertices $u, v \in V$ of $G$ are adjacent if there exists an arc $e = \left({u, v}\right) \in E$ 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).