What does the keyword `static` indicate when used with variables in C?

The keyword static, when used with variables in C, indicates that the variable retains its value between function calls. This means that a static variable is initialized only once, and its value persists for the duration of the program, regardless of the number of times the function that contains it is called. This behavior allows static variables to be useful for maintaining state information across multiple invocations of a function, making them handy for counters or storing information that needs to be preserved.

For example, if a function contains a static variable, every time that function is called, the static variable will not be reinitialized; instead, it will keep its last modified value from the previous call. This contrasts with automatic local variables, which lose their value once the function exits.

While other options relate to variables and their characteristics, they focus on different aspects. Limiting scope to the block of definition pertains to automatic variables, while fixed memory size relates to types of data. Sharing among all functions is more relevant to the concept of global variables.