Instance dungeon
In massively multiplayer online games, an instance is a special area, typically a dungeon, that generates a new copy of the location for each group, or for certain number of players, that enters the area. Instancing, the general term for the use of this technique, addresses several problems encountered by players in the shared spaces of virtual worlds. It is not widely known when instances were first used in this genre, however The Realm Online (1996) is sometimes credited as introducing the concept.
Design considerations
The problem can be stated as follows: every player wants to be "The Hero", slay "The Monster", rescue "The Princess", and obtain "The Magic Sword". When there are thousands of players all playing the same game, clearly not everyone can be the hero. The problem of everyone wanting to kill the same monster and gain the best treasure became obvious in the game EverQuest, where several groups of players would compete and sometimes harass each other in the same dungeon, in order to get to the monsters dropping valuable items. The creation of instances largely solves this set of problems, leaving only travelling to and from the dungeon as a potential risk in player versus player environments.