'Pantheistic solipsism is a technical term that has been advanced for the World as Myth idea proposed by science fiction writer Robert A. Heinlein in several of his books and stories, although the concept has little in common with either pantheism (the universe is God) or solipsism (nothing exists but my mind). Heinlein coined the phrase for the last chapter of The Number of the Beast as part of the name of a convention attended by numerous characters from different fictional universes.
The World as Myth involves the idea that a powerful author, such as Edgar Rice Burroughs, Asimov, or R.A. Heinlein himself, creates a parallel universe simply by writing about it. It incorporates the portrayal of all myths and fictional universes existing as parallel universes to our own and that persons and beings from these various “worlds” interact with one another.
For instance, in his last novels, Heinlein’s characters actually travel to and interact with the Land of Oz. Even our own world is considered an alternate (coded as "One Small Step" for the first words spoken on the moon by Neil Armstrong).
Pantheistic Solipsism is the basis for the plot of the Arnold Schwarzenegger film The Last Action Hero in which a character in an action movie crosses into the "real world". In a similar example, the movie Pleasantville features a pair of teenagers who stumble into a reality based on a popular 1950's television show. Neil Gaiman frequently uses pantheistic solipsism in his writing.'