I copied this explanation of Easter from care2.com:
Origins of Easter
The name Easter comes from Eastre, an ancient Anglo-Saxon goddess, originally of the dawn. In pagan times an annual spring festival was held in her honor. Some Easter customs have come from this and other pre-Christian spring festivals. Others come from the Passover feast of the Jews, observed in memory of their deliverance from Egypt. The resurrection of Jesus took place during the Passover. In the early days of Christianity Easter and the Passover were closely associated.
Prior to A.D. 325, Easter was celebrated on different days of the week, including Friday, Saturday, and Sunday. In that year, the Council of Nicaea was convened by emperor Constantine. They issued the Easter Rule which places Easter on the first Sunday after the first full moon on or after the vernal equinox (first day of Spring). Therefore, Easter must be celebrated on a Sunday between the dates of March 22 and April 25.
Preceding Easter Sunday is the 40-day penitential season of Lent, beginning on Ash Wednesday and concluding at midnight on Holy Saturday. Lent is a season of prayer, abstinence, and fasting. This is observed in memory of the 40 days' fast of Christ in the desert. Lent is observed for six weeks and four days by the Western Christian churches that include Saturday and Sunday into the total. In Eastern Orthodox churches Lent is 50 days since they do not count Saturdays or Sundays.
Shrove Tuesday, the day before the beginning of Lent, was designed as a way to "get it all out" before the sacrifices of Lent began. Known the world over as Mardi Gras (Fat Tuesday) or Carnival. It is celebrated in many cities, the most famous being New Orleans, LA.
Ash Wednesday, the first day of Lent, gets its name from the practice, mainly in the Roman Catholic church, of putting ashes on the foreheads of the faithful to remind them that man is but dust.
Palm Sunday: This is held on the Sunday before Easter Sunday. It recalls Jesus' triumphant entry into Jerusalem one week before his execution.
Holy Monday: commemorates Jesus' cleansing of the temple, when he assaulted money changers and overturned their tables. Some believe that this triggered his arrest and crucifixion.
Holy Tuesday: recalls Jesus' description to his disciples on the Mount of Olives of the destruction of Jerusalem.
Holy Wednesday: (once called Spy Wednesday) recalls Judas' decision to betray Jesus in exchange for 30 pieces of silver.
Maundy Thursday: commemorates the Last Supper, Jesus' agony in the garden and his arrest.
Good Friday: recalls Jesus' death on the cross. The origin of the word "good" has been lost. Some claim that it is a corruption of "God" and that the early Christians called this day "God's Friday." Others claim that "good" refers to the blessings of humanity that Christians believe arose as a result of Jesus' execution.
Holy Saturday: (a.k.a. Easter Eve) is the final day of Holy Week and of Lent.
Easter Sunday: commemorates Jesus' resurrection. In the early church, converts were baptized into church membership on this day after a lengthy period of instruction. This tradition continues today in some churches.
Many Easter symbols and customs come from the Old World.
The Cross is the symbol of the Crucifixion, as opposed to the Resurrection. However, at the Council of Nicaea, in A.D. 325, Constantine decreed that the Cross was the official symbol of Christianity. The Cross is not only a symbol of Easter, but it is more widely used, especially by the Catholic Church, as a year-round symbol of their faith.
The white lily symbolizes the Resurrection. Yet, lillies have long been revered by pagans of various lands as a holy symbol associated with reproduction. It was considered a phallic symbol!
The Easter Bunny
The Easter Bunny also originated with the pagan festival of Eastre. The goddess, Eastre, was worshipped by the Anglo-Saxons through her earthly symbol, the rabbit.
The Germans brought the symbol of the Easter rabbit to America. It was widely ignored by other Christians until shortly after the Civil War. Easter itself was not widely celebrated in America until after that time.
The Easter Egg
The exchange of eggs in the springtime is a custom that was centuries old when Easter was first celebrated by Christians. The egg was a symbol of rebirth in most cultures. Eggs were often wrapped in gold leaf or, if you were a peasant, colored brightly by boiling them with the leaves or petals of certain flowers.
Today, children hunt colored eggs and place them in Easter baskets along with the modern version of real Easter eggs -- plastic eggs filled with chocolate candy.