Piano (instrument). Keyboard instrument. The sound is produced when a depressed key strikes the strings with a felt-covered hammer, causing them to vibrate. Piano (musical instrument), stringed keyboard musical instrument, derived from the harpsichord and the clavichord. Also called the pianoforte,. The piano is the standard instrument for the equal tempered scale, yet both the high end and low end of the instrument are tuned so that they depart. This makes the grand piano a large instrument, for which the ideal setting is a spacious room with The resulting instrument is termed a pedal piano.