The Fairy type is one of the eighteen official types from the Pokémon franchise. It marked its debut in the Generation 6 games and was specifically created to tone down the Dragon type's prowess in order to make the Pokémon games more fair. The Fairy type is a somewhat cutesy, yet tricky type which attacks focus on magic, cuteness or even the moon.
Fairy is arguably one of the better defensive types, having by usual enormous Special Defense, but lacking in physical Attack and Speed. Their main resistances are Bug, Dark and Fighting, but they are also immune to Dragon-type attacks. With their high Special Attack, they will also be able to take down Dragon, Dark and Fighting, which are also weak against Fairy.
That said, the Fairy type's main weaknesses are Poison and Steel, the latter type being even more defensive than Fairy. Fairy-type moves are also resisted by Steel and Poison, as well as by the Fire type.
As of Generation 6, there are about 35 Fairy-type Pokémon, making Fairy the second rarest type in existence, right behind Ghost. 15 of these are pure Fairy type. There are about 20 Dual-typed Fairy Pokémon, but only two of them appear to be primary Fairy, making the Fairy type way more common as a secondary type. The two primary Fairy Pokémon in question, Togetic and Togekiss, are secondary Flying.
As this type debuted in Generation 6, 22 Pokémon have been changed to Fairy, or at least got the typing. A fair share used to be Normal-typed.
The Fairy type usually consists of fairies, nymphs, and other small fey-like creatures. They seem be based from traditional fairies like Clefairy or Flabébé to a more mischievous, classic kind like Klefki or Mr. Mime. Their weakness against Steel also seems to be based on fairies being weak to cold iron. A good amount of Fairy Pokémon appear to be part of the Fairy Egg Group, but there are exceptions, like Gardevoir.