As others have noted, trailing f indicates formatted output (or formatted input for functions in the scanf family).
However, I will add that the difference matters because it is important that the caller knows that the string must have the format specifier semantics. For example, do not do this:
char* s = get_some_user_input(); printf(s); // WRONG. Instead use: printf("%s", s) or fputs(stdout, s)
If s contains % characters, printing it directly with printf may cause it to access non-existent arguments, which will lead to undefined behavior (and this is the reason for some security vulnerabilities). Follow this naming convention if you ever define your own printf variational functions.