I had something more elaborate planned for today, but Real Life™ stepped in.
In American parlance, a "jumper" or a "jumper" dress is the same as a pinafore dress in British or Australian English—that is, a sleeveless dress made to be worn over a longer sleeved blouse or top.
[Left] This lovely gown is made with a blouse waist of white China silk, with a narrow pointed yoke and and a stock collar of Irish lace. The sleeves are short, reaching just below the elbows, but long sleeves can be used instead if preferred. Over this blouse is worn a most attractive over-blouse of the skirt material, a soft shade of pink chiffon broadcloth. This is edged with narrow black velvet ribbon, set off by a line of soutache braid and trimmed with tiny ball buttons.
[Right] One of the new princess jumper skirts, worn over a waist of allover lace, is illustrated on the colored plate... A fashionable green and white checked woolen was chosen for the jumper skirt, but the pattern is suited to broadcloth, cheviot, serge, Panama, as well of fancy woolens of all sorts... The waist or slip in our model is of allover Renaissance lace, but any variety of lace, China, taffeta or fancy silk, allover embroidery or lingerie can used for its development if desired.