The factorial of 5 is 120.
The factorial function works by recursively calling itself. The base case is when the input number is 0. In this case, the function returns 1. Otherwise, the function returns the product of the input number and the factorial of the input number minus 1.
Recursion is a technique in which a function calls itself. This can be used to solve problems that would be difficult to solve with a traditional iterative approach.