Fainting

In the games, fainting occurs when a Pokémon reaches 0 HP, meaning it has taken as much or more damage than they have remaining hit points. A Pokémon which has fainted is unable to battle until it has been healed.

Besides fainting from damage in a battle, a Pokémon can run out of HP due to poison while its Trainer is walking around in the field (prior to Generation IV). Pokémon can also faint instantly if their opponent successfully uses a one-hit knockout move, or may faint under certain circumstances that occur after the use of Destiny Bond or Perish Song.

Fainting will cause a Pokémon to lose happiness, and it may grow to resent its trainer if it faints often and spends a lot of time unconscious. In Pokémon Yellow, Pikachu returns to its Poké Ball when it has fainted. Though a Pokémon which has fainted cannot battle, it can still use any moves with field effects, such as Dig or HM moves like Fly.

Normal items, such as potions or status ailment healing items will not work on a fainted Pokémon. Instead, they either have to be healed at a Pokémon Center or brought back with a Revive, Max Revive, or Revival Herb.

If all of the player character's Pokémon faint, then the trainer will also faint ("<player name> Blacked/Whited Out!").

In the anime, fainting is referred to simply as being unable to battle. These Pokémon are not always unconscious, but merely do not have the energy or ability to battle, or cannot continue battling for some other reason.