Phasing in MMOs
Phasing is an MMO concept that was first introduced by World of Warcraft: Wrath of the Lich King in the Death Knight starting zone. The idea is that you go through phases in the zone that change the appearance of the zone. The places all have the same geometry but different mobs will have spawned in different places, buildings that were once upright could be burning peaces of rubble, and the army of the scourge will have advanced farther in. Phasing was created to give the player the fealing of changing the world in an MMO, which MMO's often lack. The Death Knight starting zone is currently the only place phasing is used in the MMO world, but hopefully the concept will spread to be adopted by many MMO's new or old.