The Immaterium, also colloquially known as the Haze, is the plane where magical energy comes from. It is a place of raw energy, unformed and uncontrolled. It is separated from Errai, the living world, by the Veil. A temporary small rift in the Veil is created whenever energy is drawn from the Immaterium for magic. When energy from the Immaterium is drawn through the Veil, the rift and the intent of the creator determines the shape the energy takes on Errai. The Immaterium cannot normally cross the Veil without someone creating a rift. However the exception is the Veil Scar, where the Veil separating the two worlds is broken permanently. The god Tor Dak cleaved the Skyreach mountains in ancient times and created the Scar. He had intended to free his brethren and lay waste to the other Gods and Errai. Those same feelings and intentions formed and define the Veil Scar. Thus energy that seeps through the Scar takes the form of evil creatures and demons bent on destruction and death.
The strength of the Veil waxes and wanes across the land, depending on many factors such as time of day, season, phase and alignment of the moons, local magic use, emotions, and many more. Where the Veil is weak, the Immaterium leaks through into the world, these are called Haze zones. The raw Essence can be felt by most as a heaviness in the air. The larger the leak, the greater the amount of Essence. At greater concentrations, the Essence begins to affect the body. It begins with tingling sensations, and progresses to overall muscle weakness. Mental effect are also possible from blurred visions to full on hallucinations. At high enough density, the Essence become visible as a purplish haze that hovers in the air. By this point, the Essence density is high enough to cause flesh to dissolve, blackouts, and in a few cases psychotic behavior. When the Haze becomes so dense the color turns near black and opaque, then it is guaranteed death for any who enter. The Essence eats the flesh and turns the body to mist. Needless to say people stay far away at the mere hint of a Haze zone.