Most countries around the world have the concept of a "public" holiday: a holiday that is observed across the nation and where employers are required by law to allow their staff time off.
But the lucky folk in Japan have a few more laws that go with these public holidays. For instance, if a holiday happens to fall on a Sunday one year, then the actual holiday, known as a "transfer holiday", is taken on the Monday instead. Also, if two holidays are separated by a single day, then this sandwich day is also deemed a holiday, appropriately called a "citizens holiday".
There is one such citizens holiday that is taken every year. The Japanese Greenery day falls on the 4th of May and Children's day falls on the 6th of May, thus, according to the law, the 5th of May every year is a bonus holiday for Japan.
