Triduum

A triduum (plural: tridua) is a religious observance lasting three days.

The best-known example today is the liturgical Paschal Triduum (the three days from the evening of Maundy Thursday to Easter Sunday). Other liturgical tridua celebrated in Western Christianity include the Rogation Days and the feasts of Christmas, Easter and Pentecost together with the first two days of their octaves, while the eastern churches (both orthodox and catholic) have an equal to a festive triduum when a major feast is followed by a Synaxis. The most publicly celebrated ones are the one of the feast of Epiphany together with its eve and the following day dedicated to Saint John the Baptist, and the Nativity feast with the Christmas Eve and the Synaxis of Theotokos.