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, colloquially referred to as a squeezebox. A person who plays the accordion is called an accordionist. The concertina and bandoneón are related; the harmonium and American reed organ are in the same family.
The instrument is played by compressing or expanding the bellows while pressing buttons or keys, causing pallets to open, which allow air to flow across strips of brass or steel, called reeds. These vibrate to produce sound inside the body. Valves on opposing reeds of each note are used to make the instrument's reeds sound louder without air leaking from each reed block. The performer normally plays the melody on buttons or keys on the right-hand manual, and the accompaniment, consisting of bass and pre-set chord buttons, on the left-hand manual.
The accordion is widely spread across the world. In some countries (for example Brazil, Colombia and Mexico) it is used in popular music (for example Forró, Sertanejo and B-Pop in Brazil), whereas in other regions (such as Europe, North America and other countries in South America) it tends to be more used for dance-pop and folk music and as well as in regional and is often used in folk music in Europe, North America and South America. Nevertheless, in Europe and North America, some popular music acts also make use of the instrument. Additionally, the accordion is also used in cajun, zydeco, jazz music and in both solo and orchestra performances of classical music. The piano accordion is the official city instrument of San Francisco, California. Many conservatories in Europe have classical accordion departments. The oldest name for this group of instruments is harmonika, from the Greek harmonikos, meaning harmonic, musical. Today, native versions of the name accordion are more common. These names refer to the type of accordion patented by Cyrill Demian, which concerned "automatically coupled chords on the bass side"....LESS