Easter Triduum, or Holy Triduum, is the period of three days from Holy Thursday (seen as beginning with the service of the preceding evening) to Easter Day.
Since the 1955 reform by Pope Pius XII, the Easter Triduum has been more clearly distinguished as a separate liturgical period.
After the Gloria in Excelsis Deo at the Mass of the Lord's Supper all church bells are silenced and the organ is not used until Easter Sunday when once again they are put into service.
For a list of the days and customs in the Triduum, see :
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