Prokeimenon is a liturgical term which refers to the verses chanted and sung immediately prior to the reading of the epistle and gospel lessons (although today the prokeimenon verses sung prior to the Gospel are better known as “Alleluia verses”). The word itself is derived from a Greek word meaning “that which goes before” or “precedes.” 

These verses are always taken from Holy Scripture and generally come from the Book of Psalms. They were specifically selected by the Early Church as a means of providing a joyous segue before listening to the Word of God.