Easter Triduum takes place from April 13 till April 16, 2017. Easter Triduum, Holy Triduum, Paschal Triduum, or The Three Days, is the period of three days that begins with the liturgy on the evening of Maundy Thursday and ends with evening prayer on Easter Sunday. It is the three-day period therefore from the evening of Maundy Thursday to the evening of Resurrection Sunday. Easter Triduum recalls the passion, death, burial, and resurrection of Jesus, as portrayed in the canonical Gospels.
The period that lasted from Thursday morning to before Easter Sunday began was once, in Anglo-Saxon times, referred to as "the still days". In the Catholic Church, weddings, which were once prohibited throughout the entire season of Lent and during certain other periods as well, are prohibited during the Triduum. Lutherans still discourage weddings during the entirety of Holy Week and the Triduum. (With material from: Wikipedia)