There are two recognized definitions of the term, Flag Day. The first definition is used to designate a day to fly a flag of a certain area, mostly that of nations. The second term is that a day is set aside to honor an event specifically involving a national flag (eg. creation/adoption).
Flag days are usually codified in national statutes, however, a decree by a head of state of the specific country can also order flag days. The display of the national flag on this day, mainly to fix it at either full or half staff. The locations of where the flags are flown (and how are they flown) can be also dictated by national law or decree
Different countries have a different day called Flag Day to honour their flags:
In some countries, Flag Days are special holidays on which the national flag must be flown from public buildings as required by law. Please see:
Flag Day is also the first single by The Housemartins, featured on their London 0 Hull 4 album.