When a player dies, they are instantly teleported to their spawn point with 1hp. Usually, they will leave a corpse with all their gear in the room where they died. Objects flagged as 'adhesive' will stay on the player's body, and items flagged as 'rotdeath' will disappear. Defeated players also lose 2/3 of the experience they have earned towards their next level.
Dying below level 10, or dying in an Arena room will result in keeping all your items (even rotdeath ones) and not losing any experience, although you will still be teleported back to your spawn point.
Morgues offer corpse retrieval service for a fee based on your level (level-15 x √level-15 x 100 silver). They can be found in Truce and Viorar and their services can be viewed with the 'necro' command.
A dead monster or NPC will instantly disappear from the game. They often leave a corpse but may have scripts that cause something else to happen.
Corpses are special objects similar to Containers, but can only have objects taken out and not put back in.
Player corpses have special rules associated with them. They can only be looted by their owner unless the owner has turned noloot off, or the looter is in the dead character's group. Player corpses can't be sacrificed unless they're empty.
Corpses last roughly 30 hours of game time (15 minutes of real time). Corpses decay eventually, and will eventually spill their contents so that they can be looted by anyone.
Mobile corpses can be looted by anyone, but not all mobiles leave a corpse. The 'autoloot' and 'autosac' functions usually ensure that corpses aren't left behind, however.
Zombified characters (both players and mobiles) won't necessarily die from a lethal hit, and may continue taking damage for a long while after they run out of hit points. While still helpless below 0 HP, they can recover if combat ends through some other means.