Polyphony is the style of simultaneously combining a number of parts, each forming an individual melody and harmonizing with each other.
one of the earlier styles of polyphony is Eyropen polyphony, European polyphony rose out of melismatic organum, the earliest harmonization of the chant. Twelfth-century composers, such as Léonin and Pérotin developed the organum that was introduced centuries earlier, and also added a third and fourth voice to the now homophonic chant.