The Fey are Theurgically imbued beings which occur naturally in the world. Like Wyrms, they are invisible to the Unaware. They are often classed classified as the animals of the Aware world, though the sentient Fey dislike this.
The world Fey comes from the old Hunter short-word (used for quick communication on Hunts) meaning "Kill on sight" which then fell into old English, meaning "fated to die".
Unlike in fairy tales, Fey are not just creatures such as fairies and nymphs and dryads. The category includes many Theurgic creatures as simple as the Golden Squirrel to the extremely powerful Efreet.
Since they have Theurgy flowing in their blood, they become weakened in Theurgic Voids and are extremely vulnerable to iron (since the material has the ability to cut off Theurgic flows).