Noun
triduum (plural triduums or tridua)
A period of three days (especially in Roman Catholic liturgy).
In Rome, the Chrism Mass is celebrated on Holy Thursday, but in many other parts of the world it is celebrated at another time due to the travel distances so that priests preparing for the Triduum in their parishes can also be present. Source: Internet
This reaches its climax in the celebration of the Triduum, the greatest of all liturgies, on Holy Thursday, Good Friday, and the Easter Vigil when faithful’s truly walk with Christ and enter into his saving mystery. Source: Internet