What is recursion in programming?

Recursion in programming is a technique where a function calls itself in order to solve a problem. This allows a complex problem to be broken down into smaller, more manageable sub-problems that are easier to solve. Each recursive call progresses towards a base case, which stops the recursion, ensuring that the function eventually terminates and provides a result.

For instance, consider the task of calculating the factorial of a number. A recursive function can call itself to multiply the number by the factorial of the number minus one, continuing this process until it reaches the base case of zero, where the factorial is defined to be one.

This technique is widely used in various algorithms, such as those for traversing data structures (like trees and graphs), implementing algorithms (like quicksort and mergesort), and solving mathematical problems (like the Fibonacci sequence). The elegance of recursion comes from its ability to express solutions in a clear and concise manner, making it a fundamental concept in computer science.