Parallel universe or alternative reality is a self-contained separate reality coexisting with our own. A specific group of parallel universes is called a multiverse, although this term can also be used to describe the possible parallel universes that comprise physical reality. While the terms "parallel universe" and "alternative reality" are generally synonymous and can be used interchangeably in most cases, there is sometimes an additional connotation implied with the term "alternative 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.