User blog comment:DYBAD/Character Sheet/@comment-28867799-20161208122656/@comment-4867780-20161209111934

This is mostly the product of consumerist escalation. At some point, "Multiverse" just didn't feel implressive enough anymore, so some writers pulled the world "Omniverse" instead. Then even that didn't cut it after a while, so others came up with "Totality", then "Omega Omnisphere", and so on.

Doesn't really matter though, since the meaning itself remains the same : "Fictional Continuity X". Whether you call it Marvel Multiverse or Marvel Omniverse, it's still just Marvel. Not DC, Dark Horse, Top Cow or any other non-Marvel work.