What does F4 mean in text?

Excuse me, I'm just curious, could you clarify what exactly the abbreviation "F4" stands for when used in text messaging or online communication? I've seen it being used quite often but I'm not quite sure what the actual meaning behind it is. Is it a reference to a specific function, a shortcut for a common phrase, or perhaps it's something related to a particular culture or subculture? Any insight you could provide would be greatly appreciated.