World of Warcraft (commonly known as WoW) is a massively multiplayer online role-playing game (MMORPG). It is Blizzard Entertainment's fourth game set in the fantasy Warcraft universe, which was first introduced by Warcraft: Orcs & Humans in 1994. World of Warcraft takes place within the world of Azeroth, four years after the events at the conclusion of Blizzard's previous release, Warcraft III: The Frozen Throne. Blizzard Entertainment announced World of Warcraft on September 2, 2001. The game was released on November 23, 2004, celebrating the 10th anniversary of the Warcraft franchise. It is currently the world's largest MMORPG in terms of monthly subscribers. World of Warcraft currently holds 62% of the MMOG market at 10 million subscribers. The current subscriber base for all MMOGs is 16 million. The first official expansion pack of the game, The Burning Crusade, was released on January 16, 2007. During the 2007 BlizzCon event, Blizzard announced a second expansion pack called Wrath of the Lich King on August 3, 2007.