In
computer science, a
node in the lowest level of a
tree data stucture is sometimes called a leaf.
Most nodes in a tree contain data and also refer to other nodes (via some kind of pointer). These nodes, in turn, point to still more nodes, etc, etc, creating a "tree." A leaf is a node, at the end of a path through the tree, that has no pointers to other data nodes (or, perhaps, has null pointers).
A leaf is a node that has no children and is the opposite of the root (the node that has no parent).
Note: the root can also be a leaf, but only in a tree of exactly one node.