Well, I suppose that's a jumper, but it's an awfully short one. In America a jumper is a dress with shoulder straps. It's designed to wear over a shirt. Think shirt and vest with skirt attached. I'm sure at least one person at the Lowell County Corn Festival is wearing one.
They're considered rather countrified on a grown woman. Theyr'e more common for little girls. Very practical for the "I want to wear a dress every day" phase that some girls go through.
Here's a link:
http://www.modestapparelusa.com/women/modest-dresses-and-jumpers/embroidered-denim-jumper.html