Recursion is a programming technique where a function calls itself repeatedly until a base case is met. In other words, the function is defined in terms of itself.
When a function is called recursively, it breaks down the problem into smaller sub-problems and solves them one by one. Each recursive call solves a smaller sub-problem and returns a result to the previous call. This continues until the base case is reached, which is a condition that stops the recursion and returns a value to the calling function.
Recursion is useful for solving problems that can be divided into smaller sub-problems that are similar to the original problem. For example, the factorial of a number is a problem that can be solved recursively, as it can be broken down into smaller sub-problems.