Maundy Thursday (also known as Holy Thursday, Covenant Thursday, Great and Holy Thursday, Sheer Thursday and Thursday of Mysteries) is the Christian feast, or holy day, falling on the Thursday before Easter. It commemorates the Maundy and Last Supper of Jesus Christ with the Apostles as described in the Canonical gospels. It is the fifth day of Holy Week, and is preceded by Spy Wednesday and followed by Good Friday.
The date is always between 19 March and 22 April inclusive, but these dates fall on different days depending on whether the Gregorian or Julian calendar is used liturgically. Eastern churches generally use the Julian calendar, and so celebrate this feast throughout the 21st century between 1 April and 5 May in the more commonly used Gregorian calendar. The liturgy held on the evening of Maundy Thursday initiates the Easter Triduum, the period which commemorates the passion, death, and resurrection of Christ; this period includes Good Friday, Holy Saturday, and ends on the evening of Easter. The mass or service of worship is normally celebrated in the evening, when Friday begins according to Jewish tradition, as the Last Supper was held on feast of Passover.
(... from Wikipedia on 2012-04-17 14:53:02)