The Jinn was a race descended from Adam's first wife, Lilith. Or at least that was what was believed in the Narnian universe.
The Jinn possessed innate magical abilities, sharp intellect, and extraordinary physical beauty. They once inhabited the world of Charn along with a race of Giants. Over time, the two races interbred and sired a new hybrid race that dominated Charn. Jadis, the infamous White Witch who later enslaved Narnia for a full century, was descended from this hybrid race.