Bounce

A sharp increase or uptick in approval ratings. Candidates historically go out of their convention with a 5 to 15 point increase in their approval ratings. Usually it's evanescent, and the "bounce" evaporates soon thereafter, but sometimes it's permanent. In 92, Clinton was practically unheard of until after his convention when, benefiting from Perot's quitting the race just as he was wrapping up, he went up 15 points practically overnight and went on to bury Bush I.

Nobody can explain why Kerry didn't benefit from his convention but the fact that he got no bounce from it bodes ill for his chances, to put it mildly.