Easter, Pascha, or Resurrection Day, is the most important religious feast in the Christian liturgical year. It celebrates the resurrection of Jesus, which Christians believe occurred on the third day after his crucifixion some time in the period AD 27 to 33. Many pagan elements have become part of the celebration, and those aspects are often celebrated by many Christians and non-Christians alike.

Easter also refers to the season of the church year called Eastertide or the Easter Season. Traditionally the Easter Season lasted for the forty days from Easter Day until Ascension Day but now officially lasts for the fifty days until Pentecost. The first week of the Easter Season is known as Easter Week or the Octave of Easter.

Easter is termed a movable Christian holy day because it is not fixed in relation to the civil calendar. Easter falls at some point between late March and late April each year (early April to early May in Eastern Christianity), following the cycle of the moon.

Easter is linked to the Jewish Passover not only for much of its symbolism but also for its position in the calendar. The Last Supper shared by Jesus and his disciples before his crucifixion is generally thought of as a Passover meal, based on the chronology in the Gospels. Some, however, interpreting "Passover" in John 18:28 as a single meal and not a seven-day festival, interpret the Gospel of John as differing from the Synoptic Gospels by placing Christ's death at the time of the slaughter of the Passover lambs, which would put the Last Supper slightly before Passover, on 14 Nisan of the Bible's Hebrew calendar. According to the Catholic Encyclopedia, "In fact, the Jewish feast was taken over into the Christian Easter celebration."