Easter, also called Pasch or Resurrection Sunday, is a festival and holiday celebrating the Resurrection of Jesus Christ from the dead, described in the New Testament as having occurred three days after his crucifixion by Romans at Calvary. It is the culmination of the Passion of Christ, preceded by Lent, a forty-day period of fasting, prayer, and penance.
Easter is a moveable feast, meaning it is not fixed in relation to the civil calendar. The First Council of Nicaea established the date of Easter as the first Sunday after the Paschal Full Moon, the full moon that occurs on or soonest after 21 March (taken to be the date of the equinox). Ecclesiastically, the equinox is thus reckoned to be on 21 March (although the astronomical equinox occurs on 20 March in most years), and the "Full Moon" is not necessarily on the astronomically correct date. The date of Easter therefore varies from 22 March to 25 April inclusive.