The Void Between Worlds, or just the Void, is a sort of parallel universe.
Defined more precisely by being the absence of a universe, the Void is the utter lack of any existence that separates universes, and in which they float. Though the Void does not in and on itself contain anything at all, it is possible to go there; indeed, it is necessary, if one is to cross from one universe to another. Many civilizations in many universes have found various tricks to achieve this.
Though it is by definition empty of native substance, the Void is also home to various horrors banished there from a variety of other worlds, most notably Thymon, a Lovecraftian abomination who fancies himself the Keeper of the Void itself. There also exists an Interdimensional Tavern in the Void, frequented by many travelers (and abominations). Where it came from is unknown.
Behind the scenesEdit
The Void is a fairly standard science-fiction concept.