No, not that kind of "boxing".  December 26 is celebrated as Boxing Day in the UK, tracing roots back to a tradition of the upper class giving their servants the day off after having them work on Christmas Day.  They would often give them a boxed present and a Christmas bonus.  In addition to being a bank holiday the day is marked by parades, festivals, a fox hunt or two, and what we've come to know as a "polar plunge", running & jumping in to a no doubt much too chilly body of water.

As an American I would see "Boxing Day" noted on calendars.  I always thought the day was for boxing up your unwanted gifts and returning them to stores, which is how many of us Yanks celebrate December 26.  Apparently the shopping angle has caught on across the pond too, as Boxing Day is marked with huge sales.

So, even if you're not in or from the UK, Happy "Boxing Day"...celebrate appropriately!