A Parallel Universe is a plot device commonly used in comic books. Unlike Alternate Universe, they generally still exist after they are in the story, unless they are destroyed. Parallel Universes generally are very similar except for one small difference, however this small difference is usually magnified and the repercussions of the difference are enormous. However, this is not necessarily true.

An example could be in a Marvel Universe, in which all positions of super heroes are changed. So Spider-Man could be robbing banks, and Venom could be trying to keep the peace.