Easter is a Christian holiday commemorating the resurrection of Jesus Christ from the dead three days after his crucifixion on Good Friday and marking the end of the Lent.
Easter is the holiest day in the Christian calendar, followed by Christmas and is recognized as a legal holiday in most countries with a significant Christian tradition, with the notable exception of the United States where Easter is only celebrated on Easter Sunday (and not also on Easter Monday).
The timing of Easter depends on the Jewish Pesach, in English Passover, which commemorates the sparing of the Hebrew first-born, as recounted in Exodus, since it is during this holiday that Jesus is believed to have been resurrected.
Easter and the holidays that are related to it are moveable feasts, in that they do not fall on a fixed date in the Gregorian calendar (which follows the motion of the Sun and the seasons).
Instead, they are based on a lunar calendar like that used by the Jews. At the First Council of Nicaea in 325 it was decided that Easter would be celebrated on the Sunday after the 14th day of the first lunar month of spring (in theory, the Sunday after the first full moon on or after the day of the vernal equinox). Eventually, all churches accepted the Alexandrian method of computing Easter, which set the northern hemisphere vernal equinox at 21 March (the actual equinox may fall one or two days earlier or later), and the date of the full moon was to be determined by using the Metonic cycle. A problem here is the difference between the western churches and the Eastern Orthodox Churches. The former now use the Gregorian calendar to calculate the date of Easter, while the latter still use the original Julian calendar.
In Western Christianity, Easter marks the end of the forty-six days of Lent, a period of fasting and penitence in preparation for Easter, which begins on Ash Wednesday and ends on Easter Sunday.
Lent really comprises 40 days since the 6 Sundays during this period are excluded from the Lenten fast, and are days that set apart to commemorate Easter Sunday.
The days before Easter also are special in the Christian tradition: the Sunday before is Palm Sunday, and the last three days before Easter are Maundy Thursday or Holy Thursday, Good Friday and Holy Saturday (sometimes referred to as Silent Saturday). Palm Sunday, Maundy Thursday and Good Friday respectively commemmorate Jesus's entry in Jerusalem, the Last Supper and the Crucifixion. Good Friday, Holy Saturday, and Easter Sunday are sometimes referred to as the Triduum (Latin for "Three Days"). In some countries Easter lasts two days, Sunday and Monday, called first and second Easter day, or "Easter Monday". Pentecost is seven weeks after Easter.
As with other Christian dates, Easter is also commercially important, with big sales of confectionery such as chocolate Easter eggs, marshmallow bunnies, Peeps, jelly beans, and greeting cards.
In the United States, the Easter holiday has been secularized, such that the main holiday event for many Americans is the coloring of Easter eggs, followed on Easter Sunday by an Easter egg hunt, in which young children gather the eggs that have been hidden in their homes or yards. According to the children's stories, eggs and other treats are delivered by the Easter Bunny in the form of an Easter basket which children find waiting for them when they wake up on Easter Sunday. The Easter Bunny's motives for doing this are seldom clarified.
Information largely based on Wikipedia Easter