Icon of the Resurrection, with Christ having kicked down the gates of Hades and pulling Adam and Eve out of the tombs. Christ is flanked by saints, and Satan—depicted as an old man—is bound and chained. (See Resurrection of Jesus in Christian art.)
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.
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.[nb 3] 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.