Flag day is a very minor American holiday held on June 14. On this day residents may sometimes be urged to fly the American flag, and some very few communities may hold parades.
While previously various states had celebrated flag day, it wasn't until 1916 that President Woodrow Wilson declared that flag day would be celebrated nation-wide. This was later made even more official by congress, but not made a federal holiday.
Flag day officially commemorates the adoption of the first stars and stripes flag of the United States by the Second Continental Congress on June 14, 1777. Prior to this they had continued to use a modified Union Flag, called the Grand Union Flag.
Most Americans do not really register that flag day exists, as it is fully overshadowed in the popular mind by the official day of unbounded patriotism, Independence Day (commonly referred to as the Fourth of July).