Fairy Stones were introduced in Pokémon Omega Ruby and Alpha Sapphire. They are used to evolve certain Pokémon into their Fairy-type forms.
In Pokémon X, you can find other evolution stones like the Moon Stone, Sun Stone, Dawn Stone, Shiny Stone, and Fire Stone.
If you're interested in evolving Pokémon using Fairy Stones, you'll need to play Pokémon Omega Ruby or Alpha Sapphire.