What is recursion in computer science?

Recursion in computer science is defined as a technique where a function calls itself to solve smaller sub-problems. This concept is fundamental in various programming scenarios, particularly for problems that can naturally be divided into similar sub-problems, enabling a solution to be constructed step-by-step or layer by layer.

When utilizing recursion, a function will continue to call itself with different arguments until it reaches a base case, which terminates the recursive calls. The beauty of recursion lies in its ability to simplify complex problems by breaking them down into more manageable pieces, allowing for elegant and concise code. This is commonly seen in algorithms that deal with tasks such as tree traversal, factorial calculation, and solving the Fibonacci sequence.

While other options touch upon important programming concepts, they do not accurately capture the essence of recursion. For example, statements about repeating code or increasing program efficiency may involve recursion, but they do not define it. The idea of declaring global variables is unrelated to the concept of recursion entirely, which is specifically focused on a function's ability to self-reference. Thus, the essence of recursion is best encapsulated by its definition involving the self-calling of functions to address sub-problems.