Castanets are a type of Percussion Instrument, used in Spanish, Kalo, Moorish, Ottoman, Italian, Sephardic, Swiss and Portuguese music. It is similar to an instrument called Crotalum, used in ancient Greece and Rome. There are different designs of Castanets. Castanets are used in Folkloric dances, Classical dances and Flamenco dances.
This musical instrument consists of a pair of concave shells joined in one edge by a string. Castanets are played by holding it in the hand to produce clicks of rhythmic sound of series of clicks. They are normally made of hardwood but fibreglass version is also popular. Two pairs of Castanets are used by the player usually one in each hand.
The Castanets held in right hand is called as “Maha” which is female and 1/3 higher in pitch than the one in the left hand which is called as “Macho” – male.
Here is a small video explaining Castanets.