What is recursion. Give an example

Recursion in computer science is a method where the solution to a problem depends on solutions to smaller instances of the same problem. It involves a function calling itself while a certain condition is valid. This technique allows a function to be called by itself.

A simple example of recursion could be a function in Python that calculates the factorial of a number:

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

In this example, the factorial function calls itself to calculate the factorial of a number. The base case is when n equals 1, where it returns 1. For any other value of n, it multiplies n with the factorial of n-1. This continues until the base case is reached.