Omniverse

The Omniverse -- literally " totality of all existence" is the complete extent of space of all multiverses combined. It is insurmountably vast and is the main space of action between the omniverse empires.

The Omniverse
The Omniverse, also going by the name of White Space, is an eternal void spanning infinitely in all directions with a very bright white ambient light everywhere within it. Within it are the immense amorphous black blobs that all know of as multiverses. The universes within are not truly visible, with only twinkling light able to be seen from the omniverse. This space, while the uppermost level of existence, has natural matter against all reasoning by some races, considering there is no beginning and end in temporal searches to this void. This aspect of existing forever proves to be a mystery to even the Omniverse Empires' scientists, who had long ago discovered the secret to the universe's beginning. There is also wonder as to the beginning of the multiverses, but belief is that discovering the mystery of the Omniverse will also unlock the multiverses' beginnings.

Multiverses
Multiverses, unlike the omniverse, cannot be traversed directly. Instead, they operate as networks between massive groups of countless universes for any craft with an interuniversal drive. This is the main space of operations for 99.9_ % of all life in the omniverse: Their local multiverse. The multiverses' races are typically conquering 'young' empires seeking to make a name for theirselves, which isn't easy when news doesn't travel far and reliably across countless universes to lower races. The shipboard drives that many multiverse empires use generally comes after the work on a transmitter gate for transit to another universe. The gates cannot be made as receiver only for obvious reasons of no cross universe linking of data.