a term to describe a moment when somethin that was once great has reached a point where it will now decline in quality and popularity.

Origin of this phrase comes from a Happy Days episode where the Fonz jumped a shark on waterskis. Thus was labeled the lowest point of the show.

The precise moment when you know a program, band, actor, politician, or other public figure has taken a turn for the worse, gone downhill, become irreversibly bad, is unredeemable, etc.; the moment you realize decay has set in.

The beginning of the end. Something is said to have "jumped the shark" when it has reached its peak and begun a downhill slide to mediocrity or oblivion. It's said to have been coined by Jon Hein, who has a web site, jumptheshark.com, and now a book detailing examples, especially as applied to TV shows. It supposedly refers to an episode of the TV show "Happy Days" in which Fonzie jumps over a shark on water skis, which Hein believes was the point at which the series had lost its touch and was beginning to grasp at straws.

Original meaning was the point when a television series shows it has run out of ideas and must resort to stunts to retain viewer interest. Derived from a scene in the last years of Happy Days when the Fonz waterskied over a shark. Includes actions such as "it was all a dream" episodes, live episodes, lead actors playing guest characters, and putting entire cast into a parody of some pop cultural event.

Refers to the specific moment when a TV show goes downhill. From the Happy Days episode where Fonzie overcomes his fear of sharks by jumping over one while wearing water skis.

when something stops getting better and starts getting worse

The precise moment when you know a tv show, rock band, or actor has gone downhill.