According to Christians, Jesus was resurrected three days after his crucifixion. This resurrection is celebrated on Easter Day (also Resurrection Sunday). The Easter season lasts for the fifty days until Pentecost.
Easter is a moveable holiday, meaning it does not fall on a fixed date in our Georgian calendar (which follows the cycle of the sun and the seasons). Instead, Easter is the first Sunday after the first moon whose 14th day (the ecclesiastic “full moon”) is after March 21. Therefore, Easter can fall on 35 possible dates – between March 22 and April 25 included. It last fell on March 22 in 1818, and will not do so again until 2285. It fell on March 23 in 2008, but will not do so again until 2160. Easter last fell on the latest possible date, April 25, in 1943 and will next fall on that date in 2038. However, it will fall on April 24, just one day before this latest possible date, in 2011. The cycle of Easter dates repeats after exactly 5,700,000 years, with April 19 being the most common date (source: wikipedia). Easter 2009 is April 12.
The English term Easter comes from the Old English word Ēostre. It refers to Eostur-monath, or Oster monat the April month of the Germanic calendar.