Part of Speech: Noun phrase
Meaning: No, it isn't a day we traditionally get into the ring, though children overjoyed at the bounty of Christmas might have gotten a boxing of the ears in days past. It is the first weekday following Christmas, the traditional day for giving gifts to servants and employees in the English-speaking world.
Notes: Throughout the UK, Australia, New Zealand, and Canada December 26 is still an official holiday. If the day after Christmas is Saturday or Sunday, Boxing Day is the following Monday.
In Play: Boxing Day is also known as the Feast of St. Stephen, named for the first Christian martyr. It originated in 19th century England under Queen Victoria, when it was the day "on which postmen, errand boys, and servants of various kinds received a Christmas box of contributions from those whom they serve," in the words of Charles Dickens. If you come from one of the unfortunate English-speaking nations that does not recognize Boxing Day, just remember that it comes right after "unboxing" day, Christmas.
Word History: Boxing Day is probably the day after Christmas because servants often worked on Christmas. It was called "Boxing Day" because it was the day when a box was filled with Christmas gifts and delivered to service providers. (We hope that our old friend Grogie of the Alpha Agora has had another wonderful holiday as a reward for suggesting today's very topical, seasonal phrase several years ago.)
