Recursion, in programming, is a method of problem-solving where the solution to a problem depends on smaller instances of the same problem. Recursion involves a function calling itself while a condition is met. Here's a simple example using a function that calculates the factorial of a number: ```python def factorial(n): if n == 1: return 1 else: return n * factorial(n-1) ``` This function takes in a number `n`. If `n` is 1, it returns 1 (because the factorial of 1 is 1). However, if `n` is greater than 1, the function calls itself with the argument `n-1`. This means it will continue to multiply the current number, `n`, with the factorial of `n-1` until it hits the base case, `n` equals 1, in which it stops calling itself. For example, if you call `factorial(5)`, the function unfolds like this: factorial(5) 5 * factorial(4) 5 * 4 * factorial(3) 5 * 4 * 3 * factorial(2) 5 * 4 * 3 * 2 * factorial(1) 5 * 4 * 3 * 2 * 1 120 Therefore, calling `factorial(5)` returns `120`. Note: Recursive functions need to have a base case that stops the recursion, or else they will keep calling themselves indefinitely, leading to a stack overflow error. Remember recursion is just a tool. Some problems naturally lend themselves to recursive solutions (like tree traversals or problems based on divide and conquer strategy), but that doesn't mean recursion is the best or only way to solve them.