Harmony

Harmony, in music, the simultaneous sounding of 2 or more tones or parts; also the relation and progression of chords and the rules governing their relationship. Traditional harmony is based on a 3-tone musical structure, with notes named for their position on the musical scale: the lowest tone is called the root, the middle tone is called the third (because it is the third tone above the root), and the next is called the fifth (5 tones above the root). Chords can be erected on any note of the traditional 8-note scale.