What does recursion depth refer to?

Recursion depth specifically measures the number of times a recursive function has called itself before reaching a base case or terminating condition. When a function calls itself, each call creates a new context in the call stack, and recursion depth effectively counts how many such calls are active at any given time. This concept is crucial because it directly impacts the function's performance and can lead to issues such as stack overflow if the depth becomes too great.

The correct answer highlights the nature of recursive functions and how they operate based on the principle of self-reference. Understanding recursion depth is particularly important in programming to ensure that the function can eventually reach a base case and not run indefinitely or exceed memory limits due to excessive calls.