The period itself when just one or a few players need to be eliminated before reaching the cash is referred to as the "bubble" period. The last player eliminated before the money is said either to "be the bubble" or to have "bubbled" the event.
This is the point in a tournament where the next player out does not take any winnings. The remaining players will take something away from the table. Example: The tournament you are in states that the top 25 players will win money and there are 26 players left. These 26 players are on the bubble .