When a little known nationally touring band headlines a show with a big local band. The local band plays first and draws in most of the fans who then leave after the local band finishes their set, leaving the other band playing to an empty house.
The word is derived from the City of Omaha, Nebraska, where the music fans are all asshole scenesters.
Oh man, we're playing a show at Sokol tonight with Cursive opening. I hope we don't get Omaha'd.