The place just short of the money; bust here and you get nothing.
Short stacks prioritize survival, and the chip leader uses that to attack wide. Example. In a 100-player event that pays 15 places, busting in 16th is the bubble.
At the table
In an event that pays 15 places, once 16 players remain, the play until the next bust is "the bubble." That player leaves with nothing, and the other 15 are all in the money.