The Warp

The Immaterium (also referred to as the Empyrean, the Aether, the Sea of Souls, the Realm of Chaos, Warpspace or most commonly, the Warp) is an alternate dimension of purely psychic energy that echoes and underlies the familiar four dimensions of the material universe. It is the source of all psychic powers and known instances of so-called "sorcery" or "magic" as well as the home dimension of the Chaos Gods and their myriad daemonic servants.

The Warp is most turbulent around the Imperius Galaxy, home-galaxy of the Imperium of Man, due to 4 powerful warp entities known as the Chaos Gods.