The term multiverse is used in both physics and fiction: It refers to a theoretical collection of universes that may exist alongside our own, though we cannot experience the other universes directly.
While the actual existence of a multiverse hasn't been proven, it remains an intriguing idea that suggests that our universe might be just one small bubble in a much larger reality. The term swaps the uni- prefix (meaning "one") of the word universe with multi- (meaning "many"). The concept of a multiverse is not limited to theoretical physics. It's also a storytelling device used in video games, movies, and books to explore alternate "what if" scenarios.