What is "soft pedal"

n. (context music English) The leftmost foot-pedal on most pianos which, when pushed, softens the note played.

n. a pedal on a piano that moves the action closer to the strings and so soften the sound

The soft pedal (or una corda pedal) is one of the standard pedals on a piano, generally placed leftmost among the pedals. On a grand piano this pedal shifts the whole action including the keyboard slightly to the right, so that hammers which normally strike all three of the strings for a note strike only two of them. This softens the note and also modifies its tone quality. Tone quality is also affected by forcing the remaining two strings being struck to make contact with a part of the hammer felt which is not often hit (due to the whole action being shifted); this results in a duller sound, as opposed to the bright sound which is usually produced (due to the felt being hardened from regular use).