The Plane of Shadow is a plane of existence that pervades the Material Plane. It is a world of black and white, as though color itself has been bleached from the environment.
The Plane of Shadow may be accessed and manipulated from the Material Plane through shadows. Spells cast with the Shadow Weave make use of the substance of this plane in their casting. Since some creatures use the Plane of Shadow to travel from place to place, it is often described as a transitive plane (like the Astral Plane and Ethereal Plane).
The plane is highly morphic, so buildings and geographical features are often different from their Material Plane counterparts. As such, this plane is often used as a "storage" area by those who do not want something to be openly seen. In some areas like the city of Mulsantir, the boundary between the planes is thin, and portals frequently manifest at night.
Though the Plane of Shadow is not itself evil, it is populated by a number of foul creatures who hate the light and the living, such as the fearsome nightwalkers.