You asked, "What is Armistice day?". Here in the U.S. since the late 1960's we have known it as Veterans' Day. I can remember in my youth in the 1950's pausing in school at 11:11 AM for a moment of silence on November 11, to remember those who served and died during World War I (AKA The Great War or The War to End All Wars). In the U.S. In the 60's the thinking was changed. Memorial Day, originally established to remember the deaths of those who died during the civil war (1861 to 1864) was changed to remember all those who died in the defense of their country, and Armistice Day became Veterans Day to remember all those living who served their country.
In a way, I sort of miss Armistice Day (I think in Great Britain and Canada it's called Remembrance Day). As wars go WWI was particularly horrific to those serving in the front lines. And it was nice to pause for a moment on November 11 at 11:11.
Incidently November 11, at 11:11 was the point in time the Armistice ending the hostilities went into effect.