Antiphon

An antiphon (Greek ἀντίφωνον, ἀντί "opposite" and φωνή "voice") is a short chant in Christian ritual, sung as a refrain. The texts of antiphons are usually taken from the Psalms or Scripture, but may also be freely composed. Their form was favored by St. Ambrose and they feature prominently in Ambrosian chant, but they are used widely in Gregorian chant as well.