Veterans Day is an annual American holiday honoring military veterans. A federal holiday, it is usually observed on November 11. However, if it occurs on a Sunday then the following Monday is designated for holiday leave, and if it occurs Saturday then either Saturday or Friday may be so designated.
It is also celebrated as Armistice Day or Remembrance Day in other parts of the world, falling on November 11, the anniversary of the signing of the Armistice that ended World War I. (Major hostilities of World War I were formally ended at the 11th hour of the 11th day of the 11th month of 1918 with the German signing of the Armistice.)
The holiday is commonly printed as Veteran's Day or Veterans' Day in calendars and advertisements. While these spellings are grammatically acceptable, the United States government has declared that the attributive (no apostrophe) rather than the possessive case is the official spelling. (From: Wikipedia, license: CCA-SA)