The piano is a musical instrument played by means of a keyboard. Widely used in Classical music for solo performances, ensemble use, chamber music, and accompaniment, the piano 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 world's most familiar musical instruments.

Pressing a key on the piano's keyboard causes a felt-covered hammer to strike steel strings. The hammers rebound, allowing the strings to continue vibrating at their resonant frequency. These vibrations are transmitted through a bridge to a sounding board that couples the acoustic energy to the air so that it can be heard as sound. When the key is released, a damper stops the string's vibration. Pianos are percussion instruments. According to the Hornbostel-Sachs method of music classification, they are grouped with chordophones.
This refers to the instrument's responsiveness to keyboard touch, which allows the pianist to produce notes at different dynamic levels by controlling the speed with which the hammers hit the strings.