A Level Computer Science OCR Practice Exam

Recursion in programming is characterized primarily by a function that calls itself. This self-referential function performs a specific task by breaking a problem down into smaller, more manageable instances of the same problem. Each recursive call works toward a base case that stops the recursion and begins the unraveling of those calls.

For instance, when calculating factorial numbers or traversing data structures like trees or graphs, recursion is often implemented as it simplifies complex problems by allowing the programmer to describe the solution in terms of smaller instances of the same problem.

While breaking problems into smaller parts is a characteristic of recursion, the definitive aspect is the function's self-invocation—making "a function calling itself" the most precise definition of recursion within programming contexts.