What Is Advent?
Advent on the Christian calendar is a season of preparation for the birth of Jesus. It is a season of joy leading up to Christmas Day and a time of preparation similar to Lent. Prayer, fasting, and penance are part of the Advent season. The rules are not as strict as Lent but a time of self-preparation. The purple color used on candles and vestments are associated with penance. Each Advent Sunday is meant to ready oneself for rejoicing at the birth of Jesus that is to come. The Third Sunday of Advent is the anticipatory celebration, and the color rose is used to represent joy.
The Advent wreath
Many homes and churches will have an Advent wreath to symbolize the season, and to mark each Sunday as it happens. The practice began by German Lutherans in the 18th century as a means of teaching Advent to children. The practice began to spread to Catholics and other Christian denominations as well.
Advent wreaths are circular to show that God’s love is infinite and is made with evergreen leaves. It used to be a family event to gather the leaves and make the wreath. The practice has resurfaced in recent years as many families now do this again. Advent wreaths made of artificial evergreens are available in a wide series of designs. Handmade ones can be made to last many years.
Advent: Dates, Traditions, and History(Infoplease.com)
The Catholic Encyclopedia