In C programming, a function prototype is a declaration of the function that specifies its name, return type, and parameter list. A function prototype is typically placed at the beginning of a program or in a header file, and is used to inform the compiler about the function's signature before it is used in the program.

The syntax for a function prototype in C is as follows:

return_type function_name(parameter_list);

In this syntax, return_type is the data type of the value returned by the function (or void if the function does not return a value), function_name is the name of the function, and parameter_list is a comma-separated list of parameter declarations.

Here's an example of a function prototype for a function that calculates the factorial of a number:

int factorial(int n);

In this example, the function factorial takes an integer argument n and returns an integer value, so the function prototype specifies int as the return type, factorial as the function name, and int n as the parameter list.

Function prototypes are important in C programming because they allow the compiler to check that the function is used correctly throughout the program. If a function is used before it is defined or if the function signature is incorrect, the compiler will generate an error. By using function prototypes, you can catch these errors early and avoid wasting time debugging your code. Additionally, function prototypes make your code more readable and easier to understand, as they provide a clear overview of the functions used in your program.