The Dreamlands or Dream Realm is a vast, alternate dimension or universe, accessible to earthly humans only through dreams. The waking world is our everyday or "real" universe.
The Dreamlands are for the most part a mirror-image of our waking universe, having, as far as can be determined, the same planets, stars and other cosmic geographical features. However, there are numerous races, civilizations and beings existing in the Dreamlands that do not exist in the waking universe, such as the Zoogs, Gugs, Ghasts, moon-beasts, and others. The Dreamlands also harbor numerous Cats who are very respected, to the point of being sanctified in the town of Ulthar (see The Cats of Ulthar).