Recursion is a programming technique where a function calls itself, either directly or indirectly, to solve a problem. The recursive function typically solves a smaller or simpler version of the problem, eventually reaching a base case where the solution is trivial and can be returned without further recursion.

Recursion can be a powerful and elegant way to solve problems that have a naturally recursive structure, such as traversing tree-like data structures, solving combinatorial problems, or implementing divide-and-conquer algorithms.

However, recursion can also lead to performance issues, such as stack overflow or inefficient use of memory, if not implemented correctly. It is essential to ensure that the base case is reachable and that the problem size reduces with each recursive call.

Here's a simple example of a recursive function that calculates the factorial of a number:

int factorial(int n) {
  if (n == 0) {
    return 1;
  } else {
    return n * factorial(n - 1);
  }
}