What does the term 'recursion' refer to in programming?

Recursion in programming specifically refers to a situation where a function is designed to call itself in order to break down a complex problem into smaller, more manageable instances of the same problem. This can be particularly effective for problems that can be divided into similar subproblems, such as in algorithms for sorting data or calculating factorials.

When a recursive function calls itself, it typically works toward a base case, which is a condition under which the function will stop calling itself. This process allows the function to simplify the problem progressively until it reaches a simple case that can be solved directly. It is a powerful technique that can lead to elegant solutions for problems that have a natural recursive structure. The efficiency and clarity that recursion provides can make it easier to understand the logic of complex algorithms, although it can also introduce complexity such as stack overflow if not implemented with care.

In contrast, the other options describe different behaviors that are not related to the concept of recursion—executing functions in parallel, returning values instantly, or pausing execution do not involve a function calling itself.