As of May 2015, the game "Terraria" has an official wiki at Gamepedia.com. There are also several other wikis run by fans and by magazines, such as IGN.
Gamepedia is a profesional company that hosts wikis for numerous games, but it is open to editing by anyone. However, it is an extension of Terraria Online, a large fan site that is officially supported by game developers Re-Logic. The site features over 17,000 pages, over 6,000 pages and over 220,000 registered editors.
Similar wikis include the Terraria wiki at Wikia, IGN's Terraria wiki Guide, and also the Terraria wiki at Neoseeker.