Bones

When you die, there is a chance that the level as you left it is saved, to be reloaded in a later game. Such levels are known as bones levels, bones files or simply bones.

Clues
How to tell if a level is a bones level:


 * Large concentration of different monsters
 * Wounded monsters (could be identified via a stethoscope)
 * Broken doors, holes in walls
 * Empty or partially empty throne rooms, zoos, or leprechaun halls
 * Engraved messages other than those randomly placed by NetHack
 * Few items on the floor
 * A named ghost, in a room other than a graveyard
 * Presence of corpses, which are never randomly generated (except for in the Valley of the Dead, which can have bones also)

What to do with bones
A bones level will contain some remnant of the player whose bones are laying about. Typically this is a ghost bearing the name of the player, usually stationed over the bones pile (ghosts move slowly). If the deceased player was killed by a vampire, the ghost will be replaced with a vampire bearing the name. Similarly with mummies.

Killing or luring the ghost or vampire away gives the player access to the bones. Bones piles contain the entire inventory of the player, randomly cursed. It is usually a good idea not to quaff, put on, wield, or Wear anything from a bones pile until it has been properly BUC identified, as many objects are likely to be cursed.

Beware! The original killer is still lurking about the level, probably not too far from the site of the bones. If you discover a bones pile with very advanced items, be very careful about running into whatever managed to kill your predecessor!

Item identification
Objects that the deceased player has #named will be reset to whatever description that object has in the current player's game. In other words, if the deceased had a yellow potion named "this burns when thrown" (meaning it was acid), but acid in the current player's game is a purple potion, the potion will show up as purple, without a name. The exception to this rule is fruit, which retains its name in bones piles. Engraving "Look out for the master mind flayer!" is a clever dying action to inform the bones finder about your demise.

Assuming that the game is being played on a public server such as NAO, the less scrupulous may approach the deceased player online and ask nicely what key items were being carried. This is metagaming however, and some players may not wish to oblige the bones discoverer.

Item identification via the class of the deceased
When encountering a bones level, it can be advantageous to know some details of the deceased, or at least his or her class. For example, if you find a grave with a quarterstaff, a randomly named cloak, two spellbooks, and a magic marker, you can be fairly certain the corpse is that of an early wizard, from which you can deduce that the cloak is a cloak of magic resistance. This method comes with no guarantees, but the more "indicator items" you find, the more certain you can be.

Rogues and Valkyries are hard to identify, since they both start with items common to other classes, or commonly generated.

Ineligible bones levels
These levels cannot leave bones. This list is not complete, please add to it! additionally, any level with a branch.
 * The first three levels of the dungeon (including Gnomish Mines 1 if applicable)
 * Mines End
 * Sokoban
 * Quest Home
 * Quest Goal
 * Fort Ludios
 * Medusa's Island
 * The Castle
 * Vlad's Tower, top and bottom
 * The Wizard's Tower, top and bottom
 * Fake Wizard's Tower, with portal
 * Vibrating Square
 * Moloch's Sanctum
 * The elemental planes
 * The astral plane

Note that 'special' levels may be loaded as bones at a different level than they were saved at, sometimes breaking other ad hoc rules like 'no polymorph traps before DL8'.

Ethics
Whether using the contents of a deceased player's bones is ethical is left to the player to decide. Bones can often make a difficult game much easier by providing items that the current player has not "earned" yet.

Finding one's own bones is an even more difficult position. Luckily on a public server there are enough players that this is unlikely to happen too frequently.