The Omniverse considered to be the ultimate universe of universes, which encompasses all dimensions, realities, and multiverses.
Some believe that the Omniverse is an empty void, simply the glue that holds together everything else.
Others theorize that the Omniverse is the original universe that existed and that something (or someone) forced the omniverse to be split into several different lesser universes.
In terms of the MMO Comic Index, the Omniverse includes all MMO worlds, mainstream comic worlds (for references only), and all realms mentioned or seen in comics based in MMO worlds.
(See also "Alternate Realities")