Easter, also called Pascha (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. It is the culmination of the Passion of Jesus, preceded by Lent (or Great Lent), a 40-day period of fasting, prayer, and penance.

Easter-observing Christians commonly refer to the week before Easter as Holy Week, which in Western Christianity begins on Palm Sunday (marking the entrance of Jesus in Jerusalem), includes Spy Wednesday (on which the betrayal of Jesus is mourned), and contains the days of the Easter Triduum including Maundy Thursday, commemorating the Maundy and Last Supper, as well as Good Friday, commemorating the crucifixion and death of Jesus. In Eastern Christianity, the same days and events are commemorated with the names of days all starting with "Holy" or "Holy and Great"; and Easter itself might be called "Great and Holy Pascha", "Easter Sunday", "Pascha" or "Sunday of Pascha". In Western Christianity, Eastertide, or the Easter Season, begins on Easter Sunday and lasts seven weeks, ending with the coming of the 50th day, Pentecost Sunday. In Eastern Christianity, the Paschal season ends with Pentecost as well, but the leave-taking of the Great Feast of Pascha is on the 39th day, the day before the Feast of the Ascension.

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. 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.

The English term is derived from the Saxon spring festival Ēostre; Easter is also linked to the Jewish Passover by its name (Hebrew: פֶּסַח pesach, Aramaic: פָּסחָא pascha are the basis of the term Pascha), by its origin (according to the synoptic Gospels, both the crucifixion and the resurrection took place during the Passover) and by much of its symbolism, as well as by its position in the calendar. In most European languages the feast is called by the words for passover in those languages; and in the older English versions of the Bible the term Easter was the term used to translate Passover. Easter customs vary across the Christian world, and include sunrise services, midnight vigils, exclamations and exchanges of Paschal greetings, clipping the church (England), decoration and the communal breaking of Easter eggs (a symbol of the empty tomb). The Easter lily, a symbol of the resurrection in Western Christianity, traditionally decorates the chancel area of churches on this day and for the rest of Eastertide. Additional customs that have become associated with Easter and are observed by both Christians and some non-Christians include Easter parades, communal dancing (Eastern Europe), the Easter Bunny and egg hunting. There are also traditional Easter foods that vary by region and culture.

Variable, determined by the Computus
2021 date April 4 (Western)   May 2 (Eastern)
2022 date April 17(Western)   April 24(Eastern)
2023 date April 9 (Western)   April 16 (Eastern)
2024 date March 31 (Western)  May 5 (Eastern)

In Western Christianity, using the Gregorian calendar, Easter always falls on a Sunday between 22 March and 25 April, within about seven days after the astronomical full moon. The following day, Easter Monday, is a legal holiday in many countries with predominantly Christian traditions.

Eastern Orthodox Christians base Paschal date calculations on the Julian Calendar. Because of the thirteen-day difference between the calendars between 1900 and 2099, 21 March corresponds, during the 21st century, to 3 April in the Gregorian Calendar. Since the Julian calendar is no longer used as the civil calendar of the countries where Eastern Christian traditions predominate, Easter varies between 4 April and 8 May in the Gregorian calendar. Also, because the Julian "full moon" is always several days after the astronomical full moon, the eastern Easter is often later, relative to the visible lunar phases, than western Easter.

Among the Oriental Orthodox, some churches have changed from the Julian to the Gregorian calendar and the date for Easter, as for other fixed and moveable feasts, is the same as in the Western church.