Definition:Tree (Graph Theory)/Leaf Node

Definition

Let $v$ be a node of a tree $T$.

Then $v$ is a leaf node of a $T$ if and only if $v$ is of degree $1$.

If $T$ is a rooted tree, this is equivalent to saying that $v$ has no child nodes.

A leaf node is also known as just a leaf.

In the context of rooted trees, a leaf node is often referred to as a terminal node.

In the context of more general graphs which are not trees, a degree $1$ vertex is known as a pendant vertex or an end vertex.

Consider the rooted tree below:

The leaf nodes are $2$, $4$, $6$, $8$ and $9$.