During the Renaissance what was the name composers gave to the original chant used as the basis for the main melody in a composition?

During the Renaissance, composers referred to the original chant used as the basis for the main melody in a composition as the "cantus firmus." This term designates the fixed, pre-existing melody that serves as the foundation for polyphonic music, allowing composers to build intricate harmonies and counterpoint around it. The use of cantus firmus was a significant development in the evolution of Western music during this period.