Boxing Day is specifically observed in the United Kingdom and various other regions globally, including Canada, South Africa, Australia, and New Zealand. However, it is not widely recognised in the United States. The term originates from an era when affluent individuals boxed up gifts to give to those who are poor.
Historically it was customary for the servants of wealthy individuals to work on Christmas day, catering to guests and celebrations. In appreciation for their dedicated service, employers would assemble gift boxes for the servants to take home on the day following Christmas as a token of gratitude. This practice is the origin of the term Boxing Day.
December 26 is also the feast day of Saint Stephen, the patron saint of horses, which is why Boxing Day, in the UK, became to be associated with horse racing and fox hunting. Horse racing is a Boxing Day tradition that has become an integral part of the British way of life. The meetings are not only about the horse racing, they are a chance to enjoy a get-together with family and friends, meeting and socialising, maybe placing a few bets and having a drink.
Racecourses across Britain, including the rural ones which may not normally attract as many punters, will be crammed with thousands of people. Statistics show that the average crowd at the racetrack can be boosted by four-times its normal size at the Boxing Day races.
Boxing Day traditionally was one of the main days in the fox hunting calendar, with most hunts (both mounted foxhound or harrier packs and foot packs of beagles or bassets) holding meets, often in town or village centres. The sport was banned in 2002 in Scotland and 2004 in England and Wales.

We have our sales fever too. This is Central London's Oxford Street on Boxing Day.