Fauxbourdon

Historically and properly, it is a 15th-century French technique of composition in which a plainsong melody transposed to the upper octave is notated together with a contrapuntal part moving along at the lower sixth or occasionally at the octave, while a middle part is extemporized by a singer doubling the melody at the lower fourth throughout.

In modern usage, a general designation for harmonic progressions based on parallel sixth chords such as occur not only in old music but in the works of Bach, Beethoven, and others.