Isorhythm

Isorhythm (iso or same) consists of an order of durations or rhythms, talea ("cutting", plural taleae), which is repeated within a tenor melody whose pitch content or series, color (repetition), varied in the number of members from the talea. The term was coined in 1900 by Friedrich Ludwig to describe this practice in 14th and 15th century polyphonic motets but is also used in motets of the middle ages, the music of India, and by modern composers such as Alban Berg, Olivier Messiaen, and John Cage. It may be used in all voices or only a few voices. In motets, it began in the tenor voice but was then extended to higher ones.

Source

• Hoppin, Richard H. (1978). Medieval Music. New York: W.W. Norton & Co. ISBN 0393090906.