Wild magic, or deep magic, as it is also called, is a term used to describe magic of a primordial, pre-mortal (perhaps even pre-immortal) nature. Elements of wild magic lie at the foundation of reality. While mortal practitioners can sometimes touch and use wild magic, it cannot be tamed, nor ever truly constrained or controlled.
According to the Fey Queens, the seasonal cycle of the Faerie Courts is rooted in wild magic, which grants the fey their mystical abilities. In addition to this, the Wild Hunt, with its random nature and unbridled power, is said to be one of the truest manifestations of wild magic.