Day after Christmas. Celebrated in Canada, some of South America and in other places.
Tradition has it that the "gentry" gave presents, in boxes, to their "staff" on the day after Christmas. Inferred is that they were left over, unwanted presents.
Left over presents isn't something the current generation is familiar with. My grand father always had a dozen or so generic presents wrapped but unmarked under the tree. When unexpected guests dropped by to pay their respects he would give them a present. What was left over typically went to the cook