The Thirteenth Day?
And you thought Catholics went under a rock until Easter or next December 25? Not so.
And at least when I was growing up, "the traditional end of the [Christmas] season [was] on February 2, the Feast of the Presentation of the Lord (also known as Candlemas)." This refers to "the Lord’s Presentation in the Temple by Mary and Joseph, in accordance with the canons of Mosaic Law." Meaning, they were a good Jewish couple, abiding by the practices of their religion.
Nowadays, the "end" of the Christmas season for Catholics is celebrated on "the Sunday after Epiphany, the Feast of the Baptism of Our Lord."