The Advent season encompasses the four Sundays leading up to Christ's birth on Christmas day. During this time, there are four special readings called Advent readings.
The word "Advent" comes from the Latin word adventus or "coming." Originally, Advent represented a 40-day period of fasting in preparation for the baptism of new Christians at a January feast of Epiphany, but over time, Advent became associated with Christmas time and the celebration of the first coming of Christ.
Today, instead of lasting for 40 days, the Advent season begins on whichever Sunday falls between November 27th and December 3rd and continues for four Sundays, culminating on January 6th, the feast of the Epiphany. A common advent hymn, "O Come, O Come, Emanuel," captures the meaning of the Advent season as a time when Christians look back on the first coming in celebration while awaiting the return of their savior, Jesus Christ. In a way, this is a time where Christians prepare their hearts and homes for the possibility of a second coming.
During this time, there are often candles placed throughout churches, which are symbolic of the many years Christians have been awaiting Christ's return. Common themes include love, joy, preparation and God's gift.