A persistent world or persistent state world (PSW) is a virtual world which, by the definition given by Richard Bartle, "continues to exist and develop internally even when there are no people interacting with it". The first virtual worlds were text-based and often called MUDs, but the term is frequently used in relation to massively multiplayer online role-playing games (MMORPGs) and pervasive games. Examples of persistent worlds that exist in video games include Battle Dawn, EVE Online, and Realms of Trinity.
A persistent world can be achieved by developing and maintaining a single or dynamic instance state of the game world that is shared and viewed by all players around the clock. The persistence of a world can be subdivided into "game persistence", "world persistence" and "data persistence". Data persistence ensures that any world data is not lost in the event of computer system failure. World persistence means the world continues to exist and is available to players when they want to access it. Game persistence refers to the persistence of game events within the world (a Groundhog Day MUD is a virtual world where the entire (game) world is reset periodically). When referring to a "persistent world", world and game persistence are sometimes used interchangeably. The persistence criterion is the trait that separates virtual worlds from other types of video games.
