Accordions (from 19th-century German Akkordeon, from Akkord—'musical chord, concord of sounds') are a family of box-shaped musical instruments of the bellows-driven free reed aerophone type (producing sound as air flows past a reed in a frame), colloquially referred to as a squeezebox. The essential characteristic of the accordion is to combine in one instrument a melody section, also called the diskant, usually on the right-hand manual, with an accompaniment or Basso continuo functionality on the left-hand. The musician normally plays the melody on buttons or keys on the right-hand side (referred to as the manual), and the accompaniment on bass or pre-set chord buttons on the left-hand side. A person who plays the accordion is called an accordionist. The concertina and bandoneon are related, but do not have the diskant-accompaniment duality. The harmoneon is also related and, while having the descant vs. melody dualism, tries to make it less pronounced. The harmonium and American reed organ are in the same family, but are typically larger than an accordion and sit on a surface or the floor.