Omnigender is similar to pangender, just experiencing almost all genders, but not quite all of them. Like, for example, a person can identify as Demigirl, Demiguy, Agender, and much more. It is possible to be Omnigenderfluid, it would still count as being Omnigender.
Omnigender can also be defined as someone who experiences all genders (pangender), with a preference or feeling some stronger than others.
(Not much info was known while someone was writing this. I apologize.)