At Easter (Latin pascha or Festum paschale, from Hebrew פֶּסַח pésach), Christians celebrate the feast of the resurrection of Jesus Christ.
In the early Church, Easter was celebrated as a unity of the remembrance of the Passion and the celebration of the Resurrection on Easter Vigil, the night before Easter Sunday ("Full Pascha"). From the 4th century onward, the highest feast in the church year was historically unfolded as a three-day celebration (Triduum Sacrum or Triduum paschale). Since then, therefore, in most liturgies the services have extended from the celebration of the Last Supper on Holy Thursday evening, through Good Friday with the commemoration of Jesus' suffering and death, and Holy Saturday, the day of the Lord's burial, to the dawn of the new week on Easter Sunday (liturgically Dominica Resurrectionis, "Sunday of the Resurrection" [of the Lord]).
Since, according to the New Testament, Christ's passion, death and resurrection fell during a Passover week, the date of this major movable Jewish festival also determines the date of Easter. It is determined by a lunisolar calendar and in the Western Church always falls on the Sunday after the first full moon of spring, i.e. in the Gregorian calendar at the earliest on March 22 and at the latest on April 25. The dates of the movable feast days of the Easter festival circle are also based on this.
Easter Sunday marks the beginning of the Easter period of joy (Eastertide), which lasts fifty days up to and including Pentecost. In the Middle Ages, the original triduum evolved into a separate Easter triduum, which separated the first three days of the Easter octave from the rest of the festive week. Later, this non-working period was shortened until only Easter Monday remained as a public holiday.