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.
One partridge in the pear tree, naturally, represents Jesus Christ.
Source: https://anglicancompass.com/the-12-days-of-christmas-guide-to-christmastide/