What is the functionality of a 'while loop'?

The functionality of a 'while loop' is centered around its ability to repeatedly execute a block of code as long as a specified condition remains true. This conditional execution allows for dynamic repetition based on real-time evaluations, making while loops particularly useful for scenarios where the number of iterations cannot be predetermined. For example, if you have a scenario where you want to keep prompting a user for input until they provide valid data, a while loop can evaluate the validity condition and continue executing the prompt until that condition changes to false.

In contrast, the other options outline characteristics that do not align with how a while loop operates. For instance, a loop with a fixed length would suggest a predetermined number of iterations, which defines a different kind of loop, such as a 'for loop.' Another option suggests that the code runs only once, which describes a single execution rather than a loop. Lastly, the idea that user interaction is required to start implies an external trigger rather than the self-sustaining nature of a while loop that continues based purely on its condition evaluation. Thus, the essence of a while loop lies in its conditional checks that dictate its execution flow.