"By the way, from what I'm aware, "Bonus Room" is a realtor-coined term used to describe a room in a house that can't really be considered a bedroom (maybe floor joists are spread too far apart for a conventional load, or the ceiling is angled, etc.), and that previously couldn't legally be considered as a bedroom of the finished home. It may or may not be considered part of the finished square footage, but a realtor certainly wants to point out that somone *might* be able to use the room. It may have been previously known as "storage" or "additional room" or even "useable heated attic space". Maybe it's an Ohio thing."
Where I'm building it's related to a septic field issue. You technically can have multiple bathrooms in a home, but the number of bedrooms is dictated by the septic field perc test. As long as you don't have a closet in a room it's not defined as a "bedroom" in NC. Also, a true bedroom has to have an egress window.