Answer:
ORGANUM is a term applied to medieval music that consists of Gregorian chant and one or more additional melodic lines.
Explanation:
Organum is a singing technique that finds its roots in the Middle Ages. It was a polyphonic chant that consisted of only two voices overlapped.
The first records we have of the Organum's structure is from a document called "Musica Enchiriadis", dated c. 900, from an anonymous writer.
