Harmonica is a kind of small-scale wind instrument, which uses mouth to blow or inhale to make metal reed vibrate and sound. It belongs to free spring wind instrument in instrument classification. The sound source is a reed with a length of 1.5-3.5cm, not an air column (such as a flute).

Harmonica is mainly divided into solo harmonica and ensemble harmonica, each of which has different types. The range varies slightly according to the type and tonality. As a melodic instrument, harmonica can play at least two kinds of chords. High level musicians can play two relatively independent parts at the same time on the premise of following the structure of harmonica. Because of its small size, it is called "the piano in the pocket".

Source: @marjorianne