A corpse is the body of a creature that remains after the creature dies. Corpses are relevant in Guild Wars because they can be used to resurrect fallen members, and they can be exploited by necromancers. Certain other skills, such as "I Will Avenge You!" and Signet of Capture also have effects relating to corpses.
Most creatures leave a corpse behind. However the corpses of non-fleshy creatures (such as nightmares, golems, and most minions) cannot be exploited. Some creatures, such as Kraken Spawn, leave corpses that are invisible, but still function normally. A corpse left behind by a player character, hero, henchman, animal companion (not exploitable) or boss will not go away, even if it was exploited, but the corpses of regular foes and NPC's will disappear after a minute or so.