A persistent world is a virtual fantasy world that is used as a setting for an online role-playing game. The world is always available and world events happen continually.
The persistency comes from maintaining and developing the state of the gaming world around the clock. Unlike with other games, a persistent world game's plots and events continue to develop even while some of the players are not playing their character. The comparison is to the real world where events occur that are not directly connected to a person, or continue to happen while a person sleeps, etc. Likewise, a player's character can also influence and change a persistent world. The degree to which a character can affect a world varies from game to game. (Since, the game does not pause nor create player accessible back-up files, a character's actions will have consequences that the player must deal with.)
The term gained popularity with the growth in popularity of MMORPGs.
See also