How can recursion be defined in programming?

Recursion in programming is defined as a technique where a function calls itself in order to solve a problem. This approach allows the function to break down complex problems into smaller, more manageable instances of the same problem. Each time the function calls itself, it processes a simpler version of the original task, often with a base case that stops the recursion from continuing indefinitely.

For example, in a function designed to calculate the factorial of a number, the function would call itself with a lower number until it reaches the base case of factorial zero or one, which are defined outputs. This method is highly effective for problems that exhibit a repetitive structure, enabling the programmer to create elegant solutions with less code.

The other choices describe different programming concepts that do not accurately characterize recursion. For instance, repetition without a specific termination condition doesn't involve the self-referential aspect of recursion. Collaboration among multiple functions, as mentioned in one of the options, pertains more to modular programming rather than recursion. Lastly, executing functions in a linear order represents a straightforward procedural approach rather than the self-invoking mechanism that defines recursion.