The Multiverse is a hypothetical group of multiple universes. Together, these universes comprise everything that exists. The different universes within the multiverse are called "parallel universes", "other universes", "alternate universes", or "many worlds". (quoted from wikipedia).
The APP Multiverse is a kind of collaborative fiction, similar to Round-Robin Story in which a number of authors write chapters of a novel or pieces of a story. Everyone can contribute chapters at any places in the story, so there will be numerous versions of story. This is just like parallel universes in multiverse.