Dream worlds are a commonly used plot device in fictional works, most notably in science fiction and fantasy fiction. The use of a dream world creates a situation whereby a character is placed in a marvellous and unpredictable environment and must overcome several personal problems to leave it. The dream world also commonly serves to teach some moral or religious lessons to the character experiencing it – a lesson that the other characters will be unaware of, but one that will influence decisions made regarding them. When the character is reintroduced into the real world, the question arises as to what exactly constitutes reality due to the vivid recollection and experiences of the dream world.

A fantasy world or fictional world is a world created for fictional media, such as literature, film or games. Typical fantasy worlds feature magical abilities. Some worlds may be a parallel world connected to Earth via magical portals or items ; an imaginary universe hidden within ours ; a fictional Earth set in the remote past or future ; an alternative version of our History ; or an entirely independent world set in another part of the universe.