pedal
A foot-operated lever on a piano, organ, or harp that alters the sound or pitch.
In Depth
Piano pedals are essential to the instrument's expressive range. The damper pedal (right) lifts all dampers, allowing strings to resonate freely. The una corda pedal (left) shifts the action to strike fewer strings. The sostenuto pedal (middle, on grand pianos) selectively sustains notes that are depressed when the pedal is engaged.
On an organ, pedals are an entire keyboard played by the feet, adding the lowest bass notes. Harp pedals (seven, one for each note name) raise or lower strings by a semitone, giving the instrument chromatic capability. On electric guitars, effects pedals (distortion, delay, reverb, wah-wah) process the signal between guitar and amplifier.
The average concert pianist presses the damper pedal thousands of times during a single recital — it has been called the soul of the piano because of how fundamentally it shapes the sound.