Quick scope, hmm...
Very hard to figure out on one's own, so it's quite simple.
To quick scope, is to quickly use your scope.
Commonly used throughout the sniper class, seeing as they have no crosshair, though it's quite easy to get used to, seeing as normally when firing at an opponent, you aim to the middle of the screen, as to where the crosshair is located.
So quick scoping gives you that extra bit of closure that you'll hit your target.