Excerpt from Wikipedia: Public holiday,
A public holiday, national holiday or legal holiday is a holiday generally established by law and is usually a non-working day during the year.
What are the differences between public holiday and national holiday?
Any difference between a public holiday and a national holiday definitely depends on which country you are asking about – and even the region within some countries. For most, public and national holidays are usually the same, but a public holiday can be observed on a very local level – for instance, many cities in Italy have a public holiday on the feast day of their particular patron saint, but these are not national holidays.
Over the years, we have tried to define types of holidays – http://www.officeholidays.com/about/holiday_definitions.php – but it is like herding cats at times. Canada is a good example where many of the provinces define different type of public holidays for regions and even industries. In Canada, Remembrance Day even has its own government act, which technically makes it a totally unique holiday.