Easter is a Christian holiday on which the resurrection of Jesus Christ is celebrated .
The events described in the New Testament happened in the land of Judea, conquered by the Romans. As the resurrection of Jesus Christ coincided with the Jewish Pascha festival, part of the activities during this holiday have their origins in the Old Testament of the Bible.
In most countries with dominant or considerable Christian population the days around Easter are public holidays. This is one of the reasons the Easter date must be known in advance.
There are many customs and rituals associated with Easter, e.g. colouring of eggs, making cookies etc.
Easter is preceded by about 40-day long a period of fasting  and penance . For the Western Christianity the fast starts on the Ash Wednesday , and lasts until the Easter Eve, the evening of the Easter Sunday. For the Eastern Orthodox Christianity the fasting starts 7 weeks before the Easter Sunday on the Clean Monday and the first day it is allowed to consume meat, is the Monday following the Easter Sunday  .
The date of Easter Sunday is defined as the Sunday which follows the Full Moon which follows the March equinox . This is the reason the Easter date varies from year to year. The procedure of calculation of the Easter date is quite complicated and is called Computus . There are many algorithms by which the calculation is achieved. Had the Easter did not have Christian activities, which precede it, such calculation would not be necessary, and Easter date would be based entirely on astronomical observations. However there are fasting and other activities, which start defined time before Easter Sunday, and the date of the Easter Sunday must be known well in advance.
To make things more complicated, the Schism  which divided the Eastern Orthodox Church, which uses the Julian Calendar, and the Roman Catholic Church, which uses the more accurate Gregorian Calendar . Therefore the Easter date is different for the Western Christianity and the Eastern Orthodox Christianity. In some years the Easter dates for both churches coincide.