Harmonium is a keyboard instrument, also known as peti or baja. It's similar to a reed organ. Harmonium has a European origin but was widely adapted in India during the british rule. Harmonium is mainly accompanied by a dholak or tabla. In the west, Harmonium is very popular in the Kirtan Music.
Various parts of harmonium in brief are as follows: bank of brass reeds, a pumping equipment and a keyboard. Harmoniums generally consist of one (rarely), two, three or sometimes even four sets of reeds. When air is pumped through sets of reeds, sound is produced. Air is supplied with the help of bellows which can be controlled by hands.