In tournament play, a player who's position is close to being in the money.
SoundPoker Says: Most commonly used to describe players who finished just out of a cash position. For example, if the top 16 players were in the money, the player who finished 17th would have been "on the bubble".
This term is often used in bad beat stories to describe how close a player was to winning.
See Also: Bubble, In The Money, Tournament