CHRISTMASTIDE is the 12 days from Christmas Day (December 25) to day before the Season of Epiphany starts (January 5).

“The liturgical day actually starts at sundown the night before a feast or fast. The Christmas Eve Eucharist is actually the first worship service of Christmas. The emphasis is usually on the story of the birth of Christ and the church is [decorated with green and red]. Because carols are not sung during Advent, we sing them Christmas Eve.”

While the Christmas carol, “The 12 Days of Christmas” has not been proven that it was written to help Christians learn and pass on the tenets of their faith while avoiding persecution. It is nonetheless a fun carol to learn and sing each year around this time.

• SEVENTH DAY of CHRISTMAS . . . The SEVEN SWANS a-swimming refer to the seven gifts of the Holy Spirit, the seven sacraments 
  • Wisdom
  • Understanding
  • Counsel
  • Fortitude
  • Knowledge
  • Piety
  • Fear of the Lord
• On the Sixth day of Christmas, my true love gave to me  . . . Six geese a-laying (represent the six days of creation: Day 1 – Light . . . “Then God said, Let there be light.”; Day 2 – Firmament; Day 3 – Earth, Sea, and Vegetation; Day 4 – Sun, Moon, and Stars; Day 5 – Birds and Sea Animals; Day 6 – Land Animals and Humans)
• On the Fifth day of Christmas, my true love gave to me  . . . Five golden rings (represent the first five books of the Old Testament: Genesis, Exodus, Leviticus, Numbers, and Deuteronomy)
• On the Fourth day of Christmas, my true love gave to me . . . Four calling birds (refer to the four Gospels of Matthew, Mark, Luke, and John)
• On the Third day of Christmas, my true love gave to me . . . Three french hens (stand for faith, hope, and charity)
• On the Second day of Christmas, my true love gave to me . . . Two turtle doves (refer to the Old and the New Testaments)
• On the First day of Christmas, my true love gave to me . . . A partridge is a pear tree (refers to Jesus Christ on the Cross)

Source: http://www.sharefaith.com/guide/Christian-Holidays/holiday-songs/twelve-days-of-christmas-the-song-and-the-story.html