In PvP, camping is used differently in different scenarios.
Camping a body means to stand around a corpse, mostly likely waiting for a resurrection skill to be used on it. This is a worthwhile strategy if you killed a body blocked target and wish to keep it body blocked once it resurrects, leaving you able to pressure it and kill it again. This can also be applied to a Mesmer who camps a healer body hoping to cast Blackout once it resurrects giving your team more time to kill the other healer.
Camping the resurrection shrine refers to waiting at the resurrection shrine for a number of opponents to base resurrect to quickly kill them when they may be separated from the rest of their team. This can also be effected by body blocking the resurrection shrine, waiting for invulnerability to wear off, then using area of effect skills to score multiple kills at once.
Camping a target usually means targeting a foe to accomplish a task. An example would be an interrupt Mesmer camping an enemy Elementalist, waiting for it to cast Blinding Surge so he can interrupt it.
Camping a weapon set refers to not taking advantage of weapon swapping to increase effectiveness and reduce damage depending on the situation, such as camping a vampiric weapon when blinded or not attacking or camping a shield set instead of swapping to make use of 40/40 sets when not under pressure. This is usually considered to be a sign of poor or inefficient play.
A camper is a player who camps exits, entrances, shrines or such similar places to deter, stop, or eliminate foes with a specific target in mind. An example of camping would be in Alliance Battle, a player/team watching over a teleport exit preventing or deterring the access of Kurzick/Luxon players to other shrines.