Compline..(Prayers at the End of the Day) is the final church service (or Office) of the day in the Christian tradition of canonical hours. The English word Compline is derived from the Latin completorium, as Compline is the completion of the working day. The word was first used in this sense about the beginning of the 6th century by St. Benedict in his Rule (Regula Benedicti; hereafter, RB), in Chapters 16, 17, 18, and 42, and he even uses the verb complere to signify Compline: "Omnes ergo in unum positi compleant" ("All having assembled in one place, let them say Compline"); "et exuentes a completorio" ("and, after going out from Compline...") (RB, Chap. 42).
Catholic, Eastern Orthodox, Anglican, Lutheran, and certain other Christian denominations with liturgical traditions prescribe Compline services. Compline tends to be a contemplative Office that emphasizes spiritual peace. In many monasteries it is the custom to begin the "Great Silence" after Compline, during which the whole community, including guests, observe silence throughout the night until the morning service the next day. - http://en.wikipedia.org/wiki/Compline
Great Compline is a penitential office composed of three sections, each beginning with the call to prayer, "O come, let us worship..."