(CNN) -- Celebrated on November 11 every year, Veterans Day honors men and women who have served in the U.S. armed forces. The date marks the anniversary of the end of World War I -- which ended on the 11th hour, of the 11th day, of the 11th month of 1918.
Here are some more facts behind the holiday.
By the numbers
21.5 million: The number of military veterans in the United States in 2011.
1.6 million: The number of female veterans in 2011.
2.3 million: The number of black veterans in 2011.
9.2 million: The number of veterans 65 and older in 2011. At the other end of the age spectrum, 1.8 million were younger than 35.
7.5 million: Number of Vietnam-era veterans living in 2011: 5.1 million served during the Gulf War eras (representing service from August 2, 1990, to present); 1.8 million in World War II (1941-1945); 2.4 million in the Korean War (1950-1953); and 5.4 million in peacetime only.
51,079: Number of living veterans in 2011 who served during the Vietnam era and both Gulf War eras and no other period.
Other living veterans in 2011 who served during three wars:
-- 43,942 served during World War II, the Korean War and the Vietnam era.
Living veterans in 2011 who served during two wars and no other period:
-- 876,663 served during both Gulf War eras.
-- 205,205 served during both the Korean War and the Vietnam era.
-- 129,972 served during both World War II and the Korean War.
Tomb of the Unknowns
-- November 11, 1921: The first Unknown Soldier is buried at Arlington National Cemetery.
-- 1958: Unknown Soldiers from World War II and the Korean War are buried next to the Unknown Soldier from World War I.
-- The tomb has the words inscribed, "Here rests in honored glory An American Soldier Known but to God."
-- Services are held at 11 a.m. at the Tomb of the Unknowns in Arlington National Cemetery in Arlington, Virginia, on Veterans Day. A combined color guard representing all military branches executes Present Arms at the tomb. The president lays a wreath on the tomb and a bugler plays taps.
-- 1984: An unknown soldier from Vietnam is buried in Arlington National Cemetery. He is identified through DNA tests in 1998 as Michael Blassie, a 24-year-old pilot shot down in 1972 on the border of Cambodia. His remains are disinterred and reburied in his home state of Missouri.
VFW (Veterans of Foreign Wars)
-- The VFW is a congressionally chartered, nonprofit organization.
-- It was founded in 1899 when veterans of the Spanish-American War and the Philippine Insurrection start local organizations to advocate for rights and benefits for veterans.
-- The VFW advocates rights and benefits for veterans and offers assistance to veterans, including assistance with funeral services.
-- Posts offer members a place to socialize. Bingo, fish fries, dances and inexpensive drinks have been the hallmark of VFW posts.
-- Membership is open to "all U.S. service members who have earned an overseas campaign or expeditionary medal and are currently on active duty, in the Reserves or who have been honorably discharged..."
-- The first chapters started in Ohio, Colorado and Pennsylvania.
-- 1919: President Woodrow Wilson proclaims November 11 as Armistice Day.
-- 1938: Armistice Day becomes a federal holiday.
-- June 1, 1954: President Dwight D. Eisenhower signs a bill renaming the holiday Veterans Day in order to honor all U.S. veterans.
-- 1968: Congress changes the date of Veterans Day to the fourth Monday in October.
-- September 25, 1975: President Gerald Ford changes the date of Veterans Day back to November 11. The change takes effect in 1978.