Easter,^{[nb 1]} also called Pascha^{[nb 2]} (Aramaic, Greek, Latin) or Resurrection Sunday,^{[nb 3]} is a Christian festival and cultural holiday commemorating the resurrection of Jesus from the dead, described in the New Testament as having occurred on the third day of his burial following his crucifixion by the Romans at Calvary c. 30 AD.^[12][13] It is the culmination of the Passion of Jesus Christ, preceded by Lent (or Great Lent), a 40-day period of fasting, prayer, and penance.

Easter and its related holidays are moveable feasts, not falling on a fixed date; its date is computed based on a lunisolar calendar (solar year plus Moon phase) similar to the Hebrew calendar. The First Council of Nicaea (325) established only two rules, namely independence from the Hebrew calendar and worldwide uniformity. No details for the computation were specified; these were worked out in practice, a process that took centuries and generated a number of controversies. It has come to be the first Sunday after the ecclesiastical full moon that occurs on or soonest after 21 March.^[18] Even if calculated on the basis of the more accurate Gregorian calendar, the date of that full moon sometimes differs from that of the astronomical first full moon after the March equinox.^[19]

[From Wikipedia]