The celebration of the Easter Triduum marks the end of Lent. Although the Easter Triduum is three days chronologically, it is a single liturgical day that unfolds the unity of Christ’s Paschal Mystery. It includes the three most important liturgical celebrations of the year: the Mass of the Lord’s Supper on the evening of Holy Thursday, the Liturgy of the Lord’s Passion on Good Friday at three o’clock in the afternoon, and finally, the celebration of the Resurrection of the Lord beginning at the Easter Vigil after sunset on Holy Saturday.
Of note, are the Tenebræ services that often take place these three days. Tenebræ is the name given to the service of Matins and Lauds (Office of Readings and Morning Prayer from the Divine Office) belonging to these last three days of Holy Week. Unique aspects of this liturgy are the chanting of the lamentations of Jeremiah and the use of the fifteen candle hearse. Each of the candles is extinguished during the liturgy except for one which symbolizes Christ.
By courtesy of Catholic World Report