Slang that originated from /pol/ that is used for Great Britain (mainly England) to emphasise the Muslim immigration. A mix of Britbong and *stan, which is a common suffix for Muslim ex-USSR countries.
Where user of online bulletin board or chatroom is sent when banned from the site by the moderator, usually for abusive behavior, trolling or spamming.
Troll_7462 insulted everybody he encountered on the board, so moderatorsent him to Banistan.