Classic Wiki Accordion

The accordion is a portable box-shaped musical instrument of the hand-held bellows-driven free-reed aerophone family, sometimes referred to as a squeezebox. A person who plays the accordion is called an accordionist. It is played by compressing or expanding a bellows, while pressing buttons or keys, causing valves called pallets to open which allow air to flow across strips of brass or steel called reeds that vibrate to produce sound inside the body. The instrument is sometimes considered a "one-man-band", as it needs no accompanying instrument; 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.

Source wikipedia

A musical instrument consisting of a rectangular bellows expanded and contracted between the hands. Buttons or keys operated by the player open valves, allowing air to enter or to escape. The air sets in motion free reeds, frequently made of metal. The length, density, shape, and elasticity of the reeds determine the pitch. The first accordions were made in 1822 by Friedrich Buschmann in Berlin. Bouton added a keyboard 30 years later in Paris, thus producing a piano accordion. The accordion is frequently used in folk music.

Source answers.com