A jumper dress (or jumper in American English; pinafore dress, pinafore, or pinny in British English) is a sleeveless, collarless dress intended to be worn over a blouse, shirt or sweater.

In British English, the term jumper describes a sweater. Also, in more formal British usage, a distinction is made between a pinafore dress and a pinafore, which, though a related garment, has an open back and is worn as an apron. Pinny is a shorter name for both garments.

A sundress, like a jumper, is sleeveless and collarless. However it isn't worn over a blouse or sweater, and is of a distinctly different cut and fashion.

The distinction between a jumper dress and an apron dress is unclear; in some cases, both terms are correct. If the design of the dress is directly inspired by an apron (having a bib in front, for example), the garment is often described as an apron dress.