Which of the following is NOT a national holiday?

Valentine's Day is the correct choice because it is not designated as a national holiday in the United States. National holidays are officially recognized days on which federal employees are generally given the day off work, and many private sector employees also receive paid leave.

Christmas, Independence Day, and Labor Day are all established national holidays, meaning that they are recognized by the federal government as official holidays with specific observances. Christmas is celebrated on December 25th, Independence Day marks the adoption of the Declaration of Independence on July 4th, and Labor Day is celebrated on the first Monday in September to honor the American labor movement. In contrast, Valentine's Day, celebrated on February 14th, is considered a cultural holiday focused on expressing love and affection, without official status as a national holiday.