Final answer:
The phrase 'Jump the Shark' refers to a late-series episode of the TV show 'Happy Days' when a character jumps over a shark while water skiing. This moment has become a symbol of when a TV show starts to decline in quality.
Step-by-step explanation:
The phrase 'Jump the Shark' refers to a defining moment when something once-beloved goes irretrievably downhill. It derives from a late-series episode of the TV show Happy Days. In this episode, the character Fonzie literally jumps over a shark while water skiing, which is seen as a desperate attempt to boost ratings. This moment has since become a symbol of when a TV show starts to decline in quality.