Boxing Day takes place on December 26 (the feast of St. Stephen) and is only celebrated in a few countries. It was started in the UK about 800 years ago in the Middle Ages. It was the day when the alms box (collection boxes for the poor) were opened in Parish Churches so that the contents could be distributed to poor people. A lot of Churches still have these boxes and open them on Boxing Day.
The Carol, Good King Wencelas, is set on Boxing Day and is about a King in the Middle Ages who brings food to a poor family.
It was also traditional that servants got the day off to celebrate Christmas with their families on Boxing Day. Before the second world war, it was common for working people (such as milkmen and butchers) to travel round their delivery places and collect their Christmas box or tip. This tradition has now mostly stopped and any Christmas tips, given to people such as postal workers and newspaper delivery children, are not normally given or collected on Boxing Day.
Boxing Day has now become another public holiday in countries such as the UK, Canada, Australia and New Zealand.