- from CatholicCulture.org
Although triduum can refer to any period of three days of prayer, in the Catholic Church it is most often used to refer to the three days liturgical season between Lent and Easter. The Triduum, also called the Paschal Triduum, begins on the evening of Holy Thursday and concludes on the evening of Easter Sunday. These three days commemorate Jesus’ passion, death and Resurrection as well as the institution of the Eucharist and the Priesthood. They are considered to be the holiest days of the liturgical year, and the liturgies celebrated are meant to focus our attention on the essential mysteries of our Christian faith.