Explain the use of the `static` keyword in function definitions.

The static keyword in function definitions serves to limit the visibility of the function to the file in which it is defined. When a function is declared as static, it means that its name and location are restricted to that specific file, which is particularly useful in larger programs where function names might clash. This encapsulation helps maintain modularity and prevents unintended access from other files, thus avoiding potential conflicts and enhancing code organization.

In the context of C, this is a crucial aspect of maintaining a clean and manageable codebase, especially in multilevel programming projects where multiple developers might be working on different aspects of the code concurrently. Other options might imply different functionalities of the static keyword or unrelated concepts. For instance, limiting execution time, preventing recursion, or retaining values between function calls pertain to different mechanisms within C programming and do not reflect the specific behavior of static when applied to function visibility.