You have a wonderful piece. as others have said,it is a wall mounted "outlet" At this time we were trying to standardize on a outlet. The time line is first homes had power and lights. Next some appliances came out (Toaster, iron, radio, ETC. They were screwed into a light socket. They came with a "plug" with a Edison thread on it. Later these same Edison sockets were mounted behind cover plates with a hinged door, and then things like yours.
Frank
