CORRODED SIN said:
Easy question.
If you do, you ruin the game.
(Sniping is camping by nature, and that is how you use the weapon, so you do not count. This refers to when you are using anything except a sniper rifle.)
Ambushing is also not camping. Waiting until someone goes past and shooting them in the back with ANY weapon is a perfectly valid tactic in both games and real life, and many FPS games are filled with hidey holes so you can do exactly this.
The term "camping" originates from the days of Doom and Quake, where someone would sit at one spot where an item that gave them an obvious advantage (a good weapon, quad damage, extra armour) would always respawn. So people would say "you're there so often you might as well pitch a tent", hence "camping." Camping is about exploiting the mechanics of the map in a way that doesn't translate to real-life gunplay, it is NOT about hiding and them shooting someone in the back. That's just intelligent FPS play and it's the other person's fauilt for not checking his blind spots.
Camping is also not about sitting at somewhere like a capture point and defending it. That's just intelligent defense that anyone with a brain should do.