The last finishing position in a poker tournament before entering the payout structure. He was very frustrated after getting eliminated on the bubble. Also can be applied to other situations like if six players will make a televised final table the player finishing seventh will go out on the "TV bubble". Also used to describe any situation close to the payout structure.
BUBBLE
Meaning of BUBBLE in English
Poker English dictionary. Английский словарь покера. 2012