From Bulbapedia, the community-driven Pokémon encyclopedia.
A perfect battle is a type of outcome for a Pokémon battle. The term may refer to one of three different situations.
The Pokémon Stadium series, Pokémon Colosseum, Pokémon XD and Pokémon Battle Revolution recognize a perfect battle as one where none of the Pokémon on the winning party have fainted. This definition is also recognized in the competitive battling circuit, commonly referred to as a 6-0. Perfect battles are not recognized in the core series games.
In the battle arena games, players who complete a perfect battle are rewarded with Continues ("Perfect Points" in Pokémon Battle Revolution), allowing players to fight against the same Trainer they lost to in what would usually turn out as a Game Over. Continues and Perfect Points will only last for the Cup or Colosseum challenge the player is in.
There are several alternate, unofficial definitions of a perfect battle, such as winning in the minimum amount of turns, or without taking any damage.