A sitar is a stringed instrument used in classical Indian music. Music you hear at an Indian restaurant or in a Bollywood movie probably features the distinctive twangy drone of the sitar.
Although thousands of years old, the sitar got famous in the West in the 1960s when bands like the Kinks and the Beatles used sitars in popular songs. Sitars have long necks and as many as 21 strings. It's like a guitar, but in addition to the six or seven strings that a sitar player plucks, there are more that vibrate beneath the frets, called "sympathetic strings." Despite all these strings, the word sitar means "three-stringed" in Persian.