2-Dimensional universe(s) or Two-Dimensional world(s) are the recapitulative appellation to those multiverses parallel to the universe we are living in. In fact "2-Dimensional" is an inaccurate adjective. Those multiverses also have "X" axis (length), "Y" axis (width), "Z"axis (height) just same as our universe (that's why we refer our universe as 3-Dimensional universe) but because all of our knowledge about those parallel multiverses come from characters and pictures such as novel, games, anime, comic, movies, etc. which only have "X" axis and "Y" axis, so we employed "2-Dimensional universes" as the general appellation.