Pedal point (also pedal tone, organ point, or just pedal) is a musical term describing any sustained or repeated note, usually in the bass, with changing harmonies in the other voices. The technique is often found near the end of a fugue or other polyphonic composition. Usually a pedal point is either the tonic or the dominant note, typically with some of the harmonies played above the pedal being dissonant with the pedal note. 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 a pedal division.
A double pedal is two pedal tones played simultaneously.
An inverted pedal is a pedal that is not in the bass (and often is the highest part.) Mozart included numerous inverted pedals in his works, particularly in the solo parts of his concertos.
An internal pedal is a pedal that is similar to the inverted pedal, except that it is played in the middle register between the bass and the upper voices.
Pedal points are somewhat problematic on the harpsichord or piano, which have only a limited sustain capability. Often the pedal note is simply repeated at intervals. A pedal tone can also be realized with a trill; this is particularly common with inverted pedals.
A drone differs from a pedal point in degree or quality. A pedal point may be a nonchord tone and thus required to resolve, unlike a drone, or a pedal point may simply be a shorter drone, a drone being a longer pedal point. (Courtesy of Wikipedia)