Term used in Medieval theory having several meanings:Polyphony having four vioces.The fourth voice (highest) in a polyphonic composition ( organum) having four or more voices.Diminution or augmentation by a factor of four in mensural notation. (1) the fourth voice to be composed; in organum and the early motet, it is found above the triplum, duplum/motetus, and tenor. (2) in organum, a piece which has a fourth "quadruplum" line can be called an "organum quadruplum" or "quadruplum" for short. Perotin wrote two quadrupla: "Viderunt omnes" and "Sederunt."