In the Catholic Church, Advent is a period of preparation, extending over four Sundays, before Christmas. The word Advent comes from the Latin advenio, "to come to," and refers to the coming of Christ. This refers, first of all, to our celebration of Christ's birth at Christmas; but second, to the coming of Christ in our lives through grace and the Sacrament of Holy Communion; and finally, to His Second Coming at the end of time.

Our preparations, therefore, should have all three comings in mind. We need to prepare our souls to receive Christ worthily.

First We Fast, Then We Feast:

That's why Advent has traditionally been known as a "little Lent." As in Lent, Advent should be marked by increased prayer, fasting, and good works. While the Western Church no longer has a set requirement for fasting during Advent, the Eastern Church, both Catholic and Orthodox, continues to observe what is known as Philip's Fast, from November 15 until Christmas.

Traditionally, all great feasts have been preceded by a time of fasting, which makes the feast itself more joyful. Sadly, Advent today has supplanted by "the Christmas shopping season," so that by Christmas Day, many people no longer enjoy the feast.

Note: the above information comes from Catholicism.about.com