Probably a H&R or NEF break action, single shot. These have been made in large numbers since before 1900. They have not gone through many design changes since that time, and they are still being made today. They were made to be an affordable shotgun option for folks on a budget. They work well. They are not rare. They retailed under $100 new for a long long time. It is not likely you would make much money off of one if you tried to resell it.