What term refers to comments that describe how a variable is being used in code?

The correct answer is documentation. This term encompasses a broad category of materials that provide information about the code, including how variables, functions, and classes are used. Documentation serves as a guide for developers, offering clarity on the purposes of different components within the codebase, making it easier for others (or even the original author after some time) to understand the logic and structure of the code.

Effective documentation can include inline comments, which describe what specific pieces of code are doing, as well as more extensive external documentation that outlines the overall functionality of a program or module. This helps maintain readability and fosters collaboration among programmers.

In contrast, while "annotation" can refer to an explanatory note added to a code element, it is not as comprehensive as documentation in terms of providing a full understanding of the use of variables. "Commentary" generally implies a broader analysis or discussion about the code, and "explanation" tends to refer to clarifications rather than the organized process of documenting a codebase systematically.