Altverses, also known as alternative universes. They are, in essence, alternative versions of a given specific universe. There is nothing special with that specific universe though, it's just that a baseline is convenient for defining the term "alternative" for that term poses the question: alternative to what? In essence, if the universe A is an alternative version of the universe B than the universe B is also an alternative version of the universe Many of these realities were likely formed from the Polyverse.