Available to Magikarp and Wynaut, and undoubtedly the worst move in the series of Pokemon games, Splash is a move which has no effect whatsoever.
The move has 40 PP, and does not have a rating for Power.
Rumour
Soon after the release of Pokemon Red/Blue, a rumour sprung up about Splash. According to the rumour, raising a Magikarp to a high level (around Lv60+) would make Splash actually damage a single foe: Kadabra. This rumour was quickly extinguished with the discovery of the Missingno/Rare Candy glitch.