A national day is a day on which celebrations mark the statehood or nationhood of a state or its people. It may be the date of independence, of becoming a republic, of becoming a federation, or a significant date for a patron saint or a ruler (such as a birthday, accession, or removal).
The national day is often an official public holiday. Many countries have more than one national day. Denmark and the United Kingdom are the only countries without a national day. Denmark has what is not a public holiday but an unofficial celebration called Constitution Day. National days emerged with the age of nationalism, with most appearing during the 19th and 20th centuries.