In Britain December 26th is more commonly known as Boxing Day. The reason is that until about sixty years ago many people from the lower classes worked as servants, butlers, cooks, cleaners, and nannies for the upper classes. Many other people worked in "service industries" such as delivery services, transport services, and so on. Other, young people worked as apprentices to craftsmen in various industries. These people worked long hours for low pay, and had few holidays.
Household servants were not allowed to have Christmas day off as they were needed to look after the family and guests who were celebrating Christmas. While the family and their guests would exchange presents on the 25th as equals, the 26th was the day when gifts would be given to inferiors. On Boxing Day, however, servants were able to have a holiday. They were allowed to go home to visit their families, taking with them "Christmas Boxes" of gifts - hence, the day came to be known as "Boxing Day" after the boxes that the servants were given.
Nowadays it is customary for householders to give tips, or gifts such as a bottle of whisky, to tradesmen or other workmen who make regular visits to their houses, such as the milkman, dustman, coalman, paper boy etc. These gifts are still called "Christmas Boxes" even when no box is used! However, Christmas boxes are now given during the week before Christmas, or on the last day before Christmas that the tradesman comes.
Boxing Day is usually the day when families visit relatives whom they did not see on Christmas Day.
Boxing Day is famous for two other popular activities - sports and shopping. Whereas on Christmas Day most people stay at home with their family, on Boxing Day many people like to get out and go shopping in the sales that begin on that day. Many people also go out and watch football matches and such like.
Boxing Day is also celebrated in Australia, New Zealand and Canada. In Britain Boxing Day is always on the 26th, no matter which day the 26th falls on. However, some places celebrate it on the first weekday following Christmas. So, if Christmas falls on a Friday or a Saturday Boxing Day would be celebrated on the following Monday.