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1.
A name given to a particularly harsh ban to be used in Halo Reach by game developer Bungie LLC. "Xanadu" is a portmenteau of the words "ban" and Xanadu, the mythological summer residence of Kublai Khan.
Bungie is often credited as one of the first to use the term "Banhammer", a term they use themselves, but they felt that "Banhammer" wasn't a good enough representation of just how harsh that ban is. The ban includes permanent restriction to both in-game content, online access and features on their homepage, Bungie.net.

A player or account that gets this ban is said to be sent to "Banadu".
Man, he got a one-way ticket to Banadu!
by Larsirius. May 18, 2010