Keys on a musical instrument are the levers which when depressed produce a particular pitch of note. The word may be applied to keyboard instruments such as the piano, the organ and the harpsichord, or to the metal keys on woodwind instruments such as the flute, oboe, clarinet and bassoon.
The key in which a piece of music is written indicates the scale used and the key note or home note, on the chord of which it must end. Not all music is in a key, since attempts have been made in the 20th century to extend music beyond the supposed limitations of key or tonality. It is, in any case, only the very simplest music that remains in one key throughout. Contrast is usually sought by changes of key during a composition, which will end in the key in which it began, although mode may change from major to minor (that is, a symphony in C minor may end with a movement in C major, after intervening movements in other keys). The Fifth Symphony of Beethoven, for example, is in C minor and opens with a movement in that key, followed by a slow movement in A flat major, a C minor third movement with a Trio section in C major and a last movement in C major.