The Dream include any people who live between dimensions and subsist on the essence of dreams of others.
The name of their parallel world is simply The Plane of Dreams. The occupants are all asleep, so they don’t seem to care what it’s called.
One of the Seven Peoples of the Earth, the Dream are relatively mysterious. Most of them live between known dimensions, traveling the roads between waking and sleeping, and very rarely come into contact with anyone in the waking world.
Most of the time, people who are awake can’t recall interacting with them.
They need the dreams of living beings to survive. They’re not exactly parasites, and they’re not exactly monsters, but they are very much not human, and can be nightmarish.
The Dream have one very clear wish: to be left mostly alone. When they do interact with other, it’s quietly, often with no verbal communication.
Sometimes, the Dream accidentally kidnap the dreamers they’re visiting, with disastrous consequences – there’s nothing quite like going to sleep in 1556 Holland and waking up in 912 Meso-America.
Many, many missing-persons cases are simply matter of a Dream being thoughtless, unintentionally harmful.
The Dream also have spooky control over plants, for reasons unknown. Under the control of the Dream, entire armies of trees can and have marched on their enemies like giant wooden puppets.