It means "off-topic"/general discussion, phil.

The Cat-cop used to give us all a hard time whenever we wandered off-topic so we finally invented this to protect ourselves from his wrath. If you declare yourself to be going 'OMNI' it's okay to wander off on a tangent.

You can be OMNI within a thread by discussing an ff/travel topic other than the one in the thread title, or by discussing something entirely unrelated (e.g. what sort of cat food Yaz likes, or any other 'aside'...). An entire thread can be OMNI, such as the Cats & Dogs thread from some time ago.

less confused now? Like arturo and roberto, it's one of this board's unique little wrinkles.