- (motor racing) Holding the last qualifying position with qualification still in progress, and thus liable to lose that position.
- Smith was on the bubble but lost out when Jones was faster by a tenth of a second.
- (sports) Having qualification for an event depend on the upcoming performances of other competitors.
- The Knights had been on the bubble for the tournament, but played their way in by winning their last five games.
- (idiomatic) Uncertain of success.
- The new bond issue now appears to be on the bubble, with support eroding.