Do directed cyclic graphs have leaves?

Question

Is the notion of leaf only restricted to trees?

Let's say I have a directed cyclic graph. Would it be a mistake to name the nodes having only outgoing edges leaves?

Answer 1

In undirected graphs, the common terminology is leaf for a node that has only one incident edge.

In directed graphs, the common terminology is source for a node that has no incoming edges and sink for a node that has no outgoing edges. Sometimes, if the context is clear, you will hear a sink with a single incoming edge called a leaf, but it's not as common.