Easter also called Resurrection Sunday or Pascha is one of the most important days in the Christian faith commemorating the resurrection of Jesus Christ from the dead according to the New Testament. The Easter Triduum or Paschal Triduum starts on the evening of Maundy Thursday with the last supper continuing on through Good Friday and the crucifixion and burial of Jesus Christ into Holy Saturday and ending with prayers on the evening of Easter Sunday. The day is the beginning of the Eastertide season and the end of Lent (40 days of fasting and prayer starting on Ash Wednesday ending on Holy Saturday) and Holy Week that started on Palm Sunday and lasts 7 days through to Holy Saturday. Although it is not a federal U.S. holiday, many stores are closed or operate minimal hours on this day.
Easter date each year has been determined to fall on the Sunday after the full moon following March 21 for Western Christians who use the Gregorian calendar (modern calendar). Thus Easter will fall between March 22nd and April 25th inclusive each year. For Eastern Christians who use the Julian calendar (currently runs 13 days behind Gregorian calendar) they have a similar way to determine Easter based on the first full moon after April 3rd thus Easter will fall sometime between April 4th through May 8th each year.