A jumper was a sleeveless article of clothing similar to a dress that could be worn over a shirt.
In 1953, a little girl in one of Roy Ritterhouse's drawings, Please, Take Me With You, wore a jumper. (DS9: "Far Beyond the Stars")
In 2374, Molly O'Brien planned to wear her blue jumper to the O'Brien family's picnic on the planet Golana. (DS9: "Time's Orphan")