This now iconic episode of Happy Days (Hollywood: Part 3), first broadcast on September 20, 1977. Fonzie (Henry Winkler), wearing his trademark leather jacket, jumps over a penned-in shark while water skiing.
Jumping the shark is a colloquialism coined by Jon Hein and used by TV critics and fans to denote that point in a TV show or movie series' history where the plot veers off into absurd story lines or out-of-the-ordinary characterizations, particularly for a show with falling ratings apparently becoming more desperate to draw viewers in. In the process of undergoing these changes, the TV or movie series loses its original appeal. Shows that have "jumped the shark" are typically deemed to have passed their peak.
Gary Marshall tirelessly reminds us that Happy Days went on for a number of years after the original shark jump, misunderstanding a phrase that judges suckyness, not success.