This holiday honors the U.S. flag and its history, and traditionally Americans will fly flags outside their homes, schools and businesses on this day.  Although not a “day off” from work, Congress approved the national observance of Flag Day on June 14th in 1949 to commemorate the resolution by the Continental Congress on July 14, 1777 which adopted the new nation’s flag. 

A history of the day can be found at: 

http://www.america.gov/st/pubs-english/1996/January/20050606112610pssnikwad9.374636e-02.html