Forward Declaration vs Function Prototype

[PROGR4MM3R]

Hello, I am wondering what is the key difference between these two terms listed in the title.

[MiiNiPaa]

Function prototypes are often used for forward declaration.
void foo(); //Function prototype. Used for forward declaration

However forward declaration is more encompasing:
class bar; //Forward declaration of class bar. Not a fuction prototype

[PROGR4MM3R]

okay thank you