Two to three people defending an objective together can't really be called camping, imo.
But one person sitting in a corner waiting for people (not one person, but people; throughout the game) to run by is camping.
Really? But what if there is one person sitting in the corner, one lying on the stairs and another on a balcony overlooking. All In different spots but all doing there bit to protect. And usually a lot of people come to take the objective, especially if they don't have one to protect.
I guess I call that camping because some1 can defend an objective by running around near it killing people or even just running over near the enemy base and kill them keep them distracted.
I always considered camping as some1 who sticks to one (Or multiple) spots (Not running around the field) due to some advantage either already there (Good sniper spot) or an advantage created by the player. Just my opinion.
In COD:BO One of my friends simply camps on the middle of the ground laying down (Usually next a box or grass but not always and not really using them as cover they are just there) And enemies just either don't see him/walk past him (or over him)/or they think he is a dead body. And he makes them dead, but he gets found out eventually if some1 sees him (but not always). So he just creates his own advantage.