The Veil is the name for the invisible barrier that separates the living world, Errai, from the raw unformed energies that make up the Immaterium. Legend says Errai and the Immaterium once existed in the same place, that the wild energies ravaged the seas and scarred the land. The Gods created the Veil and pulled the two planes apart to allow life to exist. Without the Veil, life would be consumed by the energies of the Immaterium.
The Veil is invisible to most people. Those who are trained in the art of sorcery are able to perceive the Veil briefly during the spell casting process when they pierce the Veil. Some spells also allow sorcerers to see the Veil temporarily. The Veil appears as a thin fog like substance that covers the land. Adept sorcerers can study the flow of the Veil and understand how the Immaterium is interacting with the world.