a service of worship in Eastern (Eastern rite church) Orthodox and Eastern-rite churches in communion with Rome that is celebrated on Wednesdays and Fridays of Lent and the first three days of Holy Week (the week preceding Easter). Initiated by the Roman pope Gregory I the (Gregory I, Saint) Great in the late 6th century AD, it was so named because the bread and wine used in the Eucharist (Holy Communion) were consecrated on the preceding Sunday.