The Blizzard WorldWide Invitational (abbreviated as WWI) is an event organized by Blizzard Entertainment to meet players, offer playable demos of future games, and offer various activities linked with Warcraft, Starcraft, and Diablo universes.
Blizzard Entertainment's convention that has traditionally taken place in the United States of America is called BlizzCon.
Going to a Blizzard Worldwide Invitational also allows players of Blizzard's games exclusive in-game extras, including the Tyrael's Hilt non-combat pet for World of Warcraft.
References
Blizzard Worldwide Invitational Wikipedia(Text) CC BY-SA