Widely used in folk music the accordian often is referred to as a squeezebox. Accordionist's play this iinstrument by compressing or expanding the bellows whilst pressing buttons or keys allowing the valves known as pallets to open. This allows the air to flow across the reeds (strips of metal) that vibrate to produce the sound.
The Chinese Cheng, which was bought to Europe in 1777, it is this musical instrument that people believe the accordion is based on.