The piano (an abbreviation of pianoforte) is a musical instrument played using a keyboard. It is widely used in classical and jazz music for solo performances, ensemble use, chamber music, accompaniment, and for composing and rehearsal. Although the piano is not portable and often expensive, its versatility and ubiquity have made it one of the world's most familiar musical instruments.
An acoustic piano usually has a protective wooden case surrounding the soundboard and metal strings, and a row of 88 black and white keys (52 white, 36 black). The strings are sounded when the keys are pressed, and silenced when the keys are released. The note can be sustained, even when the keys are released, by the use of pedals.
Pressing a key on the piano's keyboard causes a padded (often with felt) hammer to strike strings. The hammer rebounds, and the strings continue to vibrate at their resonant frequency. These vibrations are transmitted through a bridge to a soundboard that amplifies by more efficiently coupling the acoustic energy to the air. When the key is released, a damper stops the strings' vibration, ending the sound. Although an acoustic piano has strings, it is usually classified as a percussion instrument because the strings are struck rather than plucked (as with a harpsichord or spinet); in the Hornbostel-Sachs system of instrument classification, pianos are considered chordophones. With technological advances, electric, electronic, and digital pianos have also been developed.
The word piano is a shortened form of pianoforte, the Italian term for the instrument, which in turn derives from gravicembalo col piano e forte and fortepiano. The Italian musical terms piano and forte indicate "soft" and "strong" respectively, in this context referring to the variations in volume produced in response to a pianist's touch on the keys: the greater the velocity of a key press, the greater the force of the hammer hitting the strings, and the louder the sound of the note produced.