Terminal function

In a [parse_tree], each node is either a root, a branch, or a leaf. Each of these nodes can also be called a function. This type of function is different from a standard mathematical or programming function in that it does not necessarily have to taken in an argument and return a value.

A terminal function in a parse tree is a function (node) which is a leaf. A non-terminal function is a function (node) in a parse tree which is not a leaf (i.e. either a root or a branch).