After killing another player, corpse camping is where that player then continues to camp at the enemy's corpse (either by using stealth or other means) and kills them when the player resurrects themselves. Although this is frustrating to the camped player, this is not considered griefing by Blizzard and is not subject to punishment by Game Masters.
Waiting for players to resurrect at a graveyard while flagged as PvP is also considered corpse camping, even thought there technically may be no corpse.