A world in the Umbra with its own environment & physical as well as magickal laws. Most Realms have a Gauntlet of their own called a pericarp.
“Supernatural worlds are frequently sunless, for they obey none of the laws we are familiar with in our own. They may be flat, half-spheres, oval, circular, even shaped like cubes. They exist only as satellites to those realms we calll 'real,' and therefore are dependent not upon any sun or moon or planetary system for their ordering, but upon the demands - spiritual, imaginative, philosophical and so on - of worlds which do, in fact, require a sun to heat them and a moon to move their tides.” Part 2 Chapter 2 The Fortress of the Pearl by Michael Moorcock 1989