Piano

The piano is a musical instrument played by means of a keyboard. It produces sound by striking steel strings with felt hammers that immediately rebound allowing the string to continue vibrating at its resonance frequency. These vibrations are transmitted through the bridges to the soundboard, which amplifies them. The piano is widely used in Western music for solo performance, chamber music, and accompaniment. It is also very popular as an aid to composing and rehearsal. Although not portable and often expensive, the piano's versatility and ubiquity have made it one of the most familiar musical instruments. It is sometimes classified as both a percussion and a string instrument

Source: http://en.wikipedia.org/wiki/Piano