The melodica is a handheld free-reed instrument similar to a pump organ or harmonica. It features a musical keyboard on top, and is played by blowing air through a mouthpiece that fits into a hole in the side of the instrument. The keyboard usually covers two or three octaves. Melodicas are small, lightweight, and portable, and many are designed for children to play. They are popular in music education programs, especially in Asia. The modern form of the instrument was invented by Hohner in the late 1950s, though similar instruments have been known in Italy since the 19th century.

A free reed aerophone is a musical instrument that produces sound as air flows past a vibrating reed in a frame. Air pressure is typically generated by breath or with a bellows. In the Hornbostel–Sachs system, it is number: 412.13. Free reed instruments are contrasted with non-free or enclosed reed instruments, where the timbre is fully or partially dependent on the shape of the instrument body, Hornbostel–Sachs number: 42.