Easter, which celebrates Jesus Christ's resurrection from the dead, is Christianity's most important holiday. 

It has been called a moveable feast because it doesn't fall on a set date every year, as most holidays do. Instead, Christian churches in the West celebrate Easter on the first Sunday following the full moon after the vernal equinox on March 21. 

Therefore, Easter is observed anywhere between March 22 and April 25 every year. Orthodox Christians use the Julian calendar to calculate when Easter will occur and typically celebrate the holiday a week or two after the Western churches, which follow the Gregorian calendar.

The origins of the word "Easter" are not certain, but probably derive from Estre, an Anglo-Saxon goddess of spring . The German word Ostern has the same derivation, but most other languages follow the Greek term used by the early Christians: pascha, from the Hebrew pesach (Passover).

In Latin, Easter is Festa Paschalia (plural because it is a seven-day feast), which became the basis for the French Pâques, the Italian Pasqua, and the Spanish Pascua. Also related are the Scottish Pask, the Dutch Paschen, the Danish Paaske, and the Swedish Pask.