Parallel universe or alternate reality in science fiction and fantasy is a self-contained separate reality coexisting with our own. This separate reality can range in size from a small geographic region to an entire new universe, or several universes forming a multiverse. While the terms "Parallel universe" and "alternate reality" are generally synonymous and can be used interchangeably in most cases, there is sometimes an additional connotation implied with the term "alternate reality" that implies that the reality is a variant of our own. The term "parallel universe" is more general, without any connotations implying a relationship (or lack thereof) with our own universe.

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SF Sub-Genre Definitions
RandomAre you a budding sci-fi author? Do you need the many different sub genres of SF defined? A lot of people do so if you're one of them... this is where you need to look!