The Abyss is the term mortals use to describe a place that is not any place as you might understand it. It's the place beyond the Worlds of Light where Shadow rules with absolute darkness. It's the absence of form and substance as you mortals know it, an infinite realm of nothingness that sometimes shapes itself as dream and nightmare, the very opposite polarity from the Astral Plane, a place where even gods do not go to venture.
Our reality is formed of the balance of opposites, being and non-being are balanced that which is can only be finite that which is naught is infinite, yet the universe of possibilities that forms reality out of concept exists against a backdrop of the nothing. And in that nothingness lays the Abyss that which existed before reality, before the beginning of time, when beings who are not beings held eternal sway and found it…acceptable to their understanding.