Jumping the shark is a metaphor used by television critics since the 1990s. The phrase, popularized by Jon Hein on his web site www.jumptheshark.com, is used to describe the moment when a television show or similar episodic media is in retrospect judged to have passed its "peak" and shows a noticeable decline in quality. Hein also uses the "jumping the shark" concept to describe other areas of pop culture, such as music and celebrities, for whom a drastic change was the beginning of the end.
The phrase refers to a scene in a three-part episode of the American television series Happy Days broadcast in September 1977. In the "Hollywood" episode, Fonzie, wearing swim trunks and his trademark leather jacket, jumps over a tank containing a shark while on water skis. Many have noted the shark episode as the moment when they realized the show was no longer worth watching, when it became impossible to maintain a certain suspension of disbelief.