It makes you win.

NOT a way to get extra armour in World of Warcraft.

1. These keys will exit a program instead of using the exit icons.
2. A fun way to get rid of noobs in multiplayer games and chat rooms.

You press this to leave a game

The command to finish your homework quickly.
(Note: Some people will say it's a shortcut to close your application, but they are just trying to hide the truth.

Makes you fly in most video games

A statement notifying people in certain multiplayer PC games (Most notably in Team Fortress 2's Mann V. Machine game mode) to ready up for purposes of a match starting. So named because the Function-4 (F4) key starts (or reduces time of) a countdown timer for an MvM wave. Usually used for the following reasons...

1. A teammate notices a sufficiently prepared teammate who has yet to press f4 and notifies them as such.

2. An impatient scrubby try-hard 20-something who can't wait 2 1/2 minutes for a wave to start shouts it into the microphone.

3. A N00B 10-14 year-old who thinks s/he's helping when almost everyone knows about it. (often shouting into the mic in a nasally pre-teen voice.

Inversions usually occur in the following situations...

1. An engineer tells his/her team to stop the countdown so s/he can prepare sufficiently. (A competent MvM engineer can get all 4 (or 5) of his buildings ready in about 30 seconds. (usually about 50 remain after 5/6 readies))

2. A teammate needs time to figure out upgrades. (Upgrade priorities are often common sense (metal and building health upgrades for engie, UberCharge upgrades for medic, resistances and speed for scout, afterburn effectiveness for pyro, etc. with slight variance for map and loadout.)