The pump organ, reed organ, harmonium, or melodeon is a type of free-reed organ that generates sound as air flows past a vibrating piece of thin metal in a frame. The piece of metal is called a reed.

More portable than pipe organs, free-reed organs were widely used in smaller churches and in private homes in the 19th century, but their volume and tonal range are limited, and they generally had one or sometimes two manuals, with pedal-boards being rare. The finer instruments have a unique[peacock term] tone, and the cabinets of those intended for churches and affluent homes were often excellent pieces of furniture. Several million free-reed organs and melodeons were made in the USA and Canada between the 1850s and the 1920s. During this time Estey Organ and Mason & Hamlin were popular manufacturers. (source)