It's an area defined by roads, waterway, county lines etc. that is more specific to the management of that species.
So we have GMUs (Game Management Units) and those are applicable to every species. The Elk Area within that GMU might have specific rules for managing elk. Example: I live in GMU 130 but within that unit there is a deer area, 1070. That unit has antlerless tags/second deer tags that are issued only for that smaller area (Deer Area 1070).