Most Christians refer to the week before Easter as "Holy Week"—it 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 Western Christianity, Eastertide, or the Easter Season, begins on Easter Sunday and lasts seven weeks, ending with the coming of the fiftieth day, Pentecost Sunday. In Eastern Christianity, the season of Pascha begins on Pascha and ends with the coming of the fortieth day, the Feast of the Ascension.
Easter and the holidays that are related to it are moveable feasts which do not fall on a fixed date in the Gregorian or Julian calendars which follow only the cycle of the sun; rather, its date is determined on a lunisolar calendar similar to the Hebrew calendar. The First Council of Nicaea (325) established two rules, independence of the Jewish calendar and worldwide uniformity, which were the only rules for Easter explicitly laid down by the council. 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, but calculations vary.
Easter is linked to the Jewish Passover by much of its symbolism, as well as by its position in the calendar. In most European languages the feast called Easter in English is termed 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, exclaiming the Paschal greeting, clipping the church, and decorating Easter eggs (symbols of the empty tomb). The Easter lily, a symbol of the resurrection, 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 egg hunting, the Easter Bunny, and Easter parades. There are also various traditional Easter foods that vary regionally.
The modern English term Easter, cognate with modern Dutch ooster and German Ostern, developed from an Old English word that usually appears in the form Ēastrun, -on, or -an; but also as Ēastru, -o; and Ēastre or Ēostre. The most widely accepted theory of the origin of the term is that it is derived from the name of an Old English goddess mentioned by the 7th to 8th-century English monk Bede, who wrote that Ēosturmōnaþ (Old English 'Month of Ēostre', translated in Bede's time as "Paschal month") was an English month, corresponding to April, which he says "was once called after a goddess of theirs named Ēostre, in whose honour feasts were celebrated in that month".
In Latin and Greek, the Christian celebration was, and still is, called Pascha (Greek: Πάσχα), a word derived from Aramaic פסחא (Paskha), cognate to Hebrew פֶּסַח (Pesach). The word originally denoted the Jewish festival known in English as Passover, commemorating the Jewish Exodus from slavery in Egypt. As early as the 50s of the 1st century, Paul, writing from Ephesus to the Christians in Corinth, applied the term to Christ, and it is unlikely that the Ephesian and Corinthian Christians were the first to hear Exodus 12 interpreted as speaking about the death of Jesus, not just about the Jewish Passover ritual. In most of the non-English speaking world, the feast is known by names derived from Greek and Latin Pascha. Pascha is also a name by which Jesus himself is remembered in the Orthodox Church, especially in connection with his resurrection and with the season of its celebration.