What makes a function recursive?
A function which contains one or more calls to itself.
What is the purpose of the base case?
The smallest or simplest possible instance of a problem.
What is the purpose of the recursive case(s)?
What is the delegation metaphor?
No matter what function is involved, a function is involved, a function call is like calling an assistant, giving them a task, and some room to work, and waiting for them to come back with a result.