Skill Link is a Pokémon ability introduced in the fourth generation. It maximizes the number of attacks in multihit moves. It was the signature ability of Cloyster until Generation V.
Skill Link makes multistrike moves always hit their maximum number of hits. For Generation IV, this only applied to moves that can hit up to 5 times but Generation V added Triple Kick so, the move only had one accuracy check instead of for each hit. Additionally, if the ability is lost in the middle of an attack, the number of attacks is still 5.