Prokeimenon
In the liturgical practice of the Orthodox Church and Byzantine Rite, a prokeimenon (Greek Προκείμενον, plural prokeimena; sometimes prokimenon/prokimena; lit. "that which precedes") is a psalm or canticle refrain sung responsorially at certain specified points of the Divine Liturgy or the Divine Office, usually to introduce a scripture reading. It corresponds to the Gradual of the Roman Mass.