The Multiverse
"Many similar universes co-exist in the same space, but in an infinite number of different dimensions! There's no limit to the variations..." - Superboy (SB No.117, Dec 1964)
The sum total of all universes referred to collectively.
Numerous parallel worlds and universes have been documented. These universes are usually designated by the the version of the earth that exist in them. So the universe which is home to the villainous analogue of Superman, Ultraman, is designated Earth-3 and the alternate universe created by the villainous Johnny Thunder of Earth-1 in which Superman and the other members of the Justice League of America do not exist is known as Earth-A.
There are at least two similar versions of Superman, one from a world designated Earth-1 and the other from a world designated Earth-2. These two men while very similar have different histories and are clearly different people as demonstrated by the fact that they have met on occasion.
The man most people know as Superman is in fact the Superman of Earth-1 though it is claimed by some Superman historians that the earliest chronicles of the Man of Steel, approximately 1938-1955, are actually those of the Superman of Earth-2.
