Can you explain the concept of recursion and provide an example of a recursive function you have implemented in Python?

Recursion is a programming technique where a function calls itself in order to solve a problem. It's often used for tasks that can be broken down into smaller, similar subproblems. Here's an example of a recursive function to calculate the factorial of a number:

def factorial(n):
    if n == 0:
        return 1
    else:
        return n * factorial(n - 1)

# Usage
print(factorial(5))  # Output: 120

In this example, the factorial() function calls itself with a smaller argument until it reaches the base case (n == 0), then returns the result back through the call stack.