Mechanically, the sitar is a fairly complicated musical instrument. It bears sympathetic strings (strings which are tuned, but not plucked - they simply vibrate and hum when the strings nearby are played), as well as movable frets. and over 20 strings! The sitar is tuned to a classical raga, or scale, and is played with a pick called a mezrab.
The sitar gained popularity in the western world when Beatle George Harrison learned to play from master Ravi Shankar and incorporated the instrument into several Beatles songs.