Definition:Arborescence/Definition 1

Definition
Let $G = (V, A)$ be a directed graph.

Let $r \in V$.

Then $G$ is an arborescence of root $r$, an $r$-arborescence, or just an arborescence iff:


 * For each $v \in V$ there is exactly one directed walk from $r$ to $v$.

Also see

 * Equivalence of Definitions of Arborescence