Triduum
Also, "Easter Triduum," "Pascal Triduum" or "Holy Triduum"
"Triduum"
- from tri- (three) + duum (days), thus "a period of three days"
The Paschal Triduum is the "Feast of feasts" celebrating the Lord's Passion and Resurrection
- from the Catechism entry on the "liturgical year", which begins at the Easter Triduum:
Beginning with the Easter Triduum as its source of light, the new age of the Resurrection fills the whole liturgical year with its brilliance. Gradually, on either side of this source, the year is transfigured by the liturgy. It really is a "year of the Lord's favor." The economy of salvation is at work within the framework of time, but since its fulfillment in the Passover of Jesus and the outpouring of the Holy Spirit, the culmination of history is anticipated "as a foretaste," and the kingdom of God enters into our time. Therefore Easter is not simply one feast among others, but the "Feast of feasts," the "Solemnity of solemnities," just as the Eucharist is the "Sacrament of sacraments" (the Great Sacrament). St. Athanasius calls Easter "the Great Sunday"43 and the Eastern Churches call Holy Week "the Great Week." The mystery of the Resurrection, in which Christ crushed death, permeates with its powerful energy our old time, until all is subjected to him. (CCC 1168-69)
See