It refers to the practice, in times past, of giving a gift to the servants and regular tradespeople on the day after Christmas. This gift became known, generically, as "the Christmas box" and the day as "Boxing Day."
To a minor extent, the practice exists in some eastern U.S. cities where giving the mailman or building super a holiday gift is the norm. The practice exists, but the name does not.
All Grinch sympathizers can breathe a sigh of relief. They'll not hear a carol or see a red suit trimmed in white fur for 10 months or so.
BTW, this was the first Christmas season in living memory during which I did not see a TV ad for the Salad Shooter or Ronco Vegematic. Next stop: New Years Eve and Day.
