Easter (Greek: ?????, Pascha or Pasxa) is the most important religious feast in the Christian liturgical year.Anthony Aveni, "The Easter/Passover Season: Connecting Time's Broken Circle," The Book of the Year: A Brief History of Our Seasonal Holidays (Oxford: Oxford University Press, 2004), 64-78.

Christians believe that Jesus was resurrected from the dead two daysThis resurrection is commonly said to have occurred "on the third day", including the day of crucifixion. after his crucifixion, and celebrate this resurrection on Easter Sunday, two days after Good Friday. The year of this resurrection is variously estimated between the years AD 26 and 36 (see also Chronology of Jesus). Many non-Christian cultural elements, such as the Easter Bunny, have become part of the holiday, 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 also marks the end of Lent, a season of prayer and penance.

Easter is termed a moveable feast 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. After several centuries of disagreement, all churches accepted the computation of the Alexandrian Church (now the Coptic Church) that Easter is the first Sunday after the Paschal Full Moon, which is the first moon whose 14th day (the ecclesiastic "full moon") is on or after March 21 (the ecclesiastic "vernal equinox").

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 as a single meal and not an eight-day festival, (Notes on John 13:2, John 18:28, and John 19:14.) 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 lamb, which would put the Last Supper slightly before Passover, on Nisan 14 of the Bible's Hebrew calendar. According to the Catholic Encyclopedia, "In fact, the Jewish feast was taken over into the Christian Easter celebration."