Ha, thats a pretty good question. I haven't looked at it in a way where someone might not know what is meant.
There are several different geese, so I guess it is easier to lump them into 2 categories. Light geese are all under the same bag limits.
"Light geese" = snow geese and blue geese (same species, different color) and ross's geese (looks similar to a snow goose, but smaller)
"Dark Geese" = Canada Geese, cackling geese (looks like a canada goose, but smaller), and white-fronted geese (speckle bellies)