Pedal point

In music, a pedal point (also pedal note, organ point, pedal tone, or pedal) is a sustained tone, typically in the bass, during which at least one foreign (i.e. dissonant) harmony is sounded in the other parts. A pedal point sometimes functions as a "non-chord tone", placing it in the categories alongside suspensions, retardations, and passing tones. However, the pedal point is unique among non-chord tones, "in that it begins on a consonance, sustains (or repeats) through another chord as a dissonance until the harmony", not the non-chord tone, "resolves back to a consonance".[2]

Pedal point example. Play 
Pedal tone example. The repeated d in the first bar is the pedal point.[1] Play 

Pedal points "have a strong tonal effect, 'pulling' the harmony back to its root".[2] When a pedal point occurs in a voice other than the bass, it is usually referred to as an inverted pedal point[3] (see inversion). Pedal points are usually on either the tonic or the dominant (fifth note of the scale) tones. The pedal tone is considered a chord tone in the original harmony, then a nonchord tone during the intervening dissonant harmonies, and then a chord tone again when the harmony resolves. A dissonant pedal point may go against all harmonies present during its duration, being almost more like an added tone than a nonchord tone, or pedal points may serve as atonal pitch centers.

The term comes from the organ for its ability to sustain a note indefinitely and the tendency for such notes to be played on an organ's pedal keyboard. The pedal keyboard on an organ is played by the feet; as such, the organist can hold down a pedal point for lengthy periods while both hands perform higher-register music on the manual keyboards.