Ascian is a broad term referring to people of a generally nomadic hunter-gatherer ancestry that at least superficially resembles Native American cultures in the real world. They exist outside the clan system and are frequently depicted as holding low social and economic status, particularly in the domed cities.
While it is tempting to refer to them as "aboriginal", their origins are unclear. Chief Coward directly speculates on the relationship between Ascians and the people of the domes in a flashback during King Of The Cats (storyline) - "Did they come from us? Or we from them?"