1.

Function return as void

There are various functions in C which do not return any value or you can say they return void. A function with no return value has the return type as void. For example, void exit (int salary);

2.

Function argument as void

There are various functions in C which do not accept any parameter. A function with no parameter can accept a void. For  example, int rand(void);

3.

Pointers to void

A pointer of type void * represents the address of an object, but not its type. For example, a memory allocation function void *malloc(size_t size); returns a pointer to void which can be cast to any data type.