In some countries, mainly those with a more hard and fast class or caste system I think (and also mainly those with their origins in the so called British Commonwealth), today is called Boxing Day. That's where higher class people in those countries provide small gift boxes (hence the name) to the lower class tradespeople and servants (mailman, blacksmith, chemist, housekeeper, gardener, etc.) in those countries, and bosses do the same for their employees.
It is usually the first business day after Christmas Day, since this is (conveniently) when the higher classes will next encounter the lower classes. One could say that, technically, Christmas Day is Boxing Day Eve (most of the time), giving the latter psychologically more import, the same way that Christmas Eve is a slightly inferior holiday compared with Christmas Day. If you were a particularly passive aggressive sort of blue collar worker, this might give you a smug sense of satisfaction as your Overlords bestow their trinkets and regifted items upon you.
Boxing day has origins that are somewhat distressing to those of us who view all people as having equal worth. In ancient times, servants were expected to wait on their masters during Christmas day feasts and were then sent home to be with there own families the next day, taking with them small gifts, money, or even just leftover food, in exchange for their subservience.
In some countries, Boxing Day has become a shopping frenzy similar to Black Friday in the United States, where retailers have large sales with the lowest prices of the year. This is economically wise, since the period after Christmas tends to be a time of slower retail sales, so this gives retailers a little financial bump going into the commercial doldrums of January and February. Boxing Day is also the biggest day for unwanted gift returns and exchanges in these countries, which may undo any benefit from the shopping rush.
Some countries have laws forbidding shops to open on Boxing Day.