The Harmonium is not native to South Asia – French missionaries introduced it to India during the colonial period. Today is widely used as an accompanying instrument in all forms of Indian music, be they classical, devotional or film music.
The Harmonium is a small, tabletop size organ with bellows at the back that are pumped by one hand while the other hand plays the keyboard, resembling the black and white keys of the piano. It contains multiple chambers inside with different banks of free reeds in each chamber which vibrate when air passes through them giving the Harmonium its sound.
The body is the wooden box that contains the various parts of the Harmonium. The Indians have developed numerous variations of the Harmonium, including those with moveable keyboards and those that fold away for easy transport. Most Harmoniums have numerous buttons, stops and levers allowing the player to choose different sets of reeds to play individually or in unison.
You might see harmonium commonly used in Hindu, Sikh and Islamic sufi devotional music.