Fairy was introduced as a new Pokémon type in Pokémon X and Y.
Pokémon X and Y were released worldwide for the Nintendo 3DS on October 12, 2013. Their introduction of the Fairy type was the first addition of a new type since Gold and Silver introduced Dark and Steel in 1999.
Fairy-type Pokémon and moves were designed partly to rebalance battles. The type is super effective against Dragon, Fighting, and Dark Pokémon, while Fairy Pokémon are weak to Poison and Steel attacks. Several older Pokémon, including Jigglypuff, Marill, and Gardevoir, were retrospectively given the Fairy type.
The addition brought the total number of Pokémon types to 18. It is easy to confuse Fairy with a move or evolution mechanic, but Fairy is a full elemental type used in Pokémon species, attacks, abilities, and battle calculations.