The Void is part of the Dungeons & Dragons cosmology, and first appeared with the introduction of Planescape. It is a place, which exists between the planes, and touches everything.

The Void, despite its name is neither empty, nor uninhabited but is composed, mostly, of nothingness. Certain individuals are able to utilize the Void for power (such as the Player Class: Void Disciple), but any direct interaction with it is touchy, at best, and only experienced mages or planar travelers should attempt at going there.

Some campaigns also feature the Void as a place outside the known universe that also touches within in. In such contexts, the Void may be timeless, or have erratic time as per planar time rules. In any event, the Void is without air, heat, and usually without magic, though supposedly psionics work there.

The Void is also one of the cards in the Deck of Many Things. This card sends a character's soul to some other desolate location, leaving his body in a catatonic state and forcing the adventuring party to find a way to rescue the soul.[1]