Also Armistice Day, or Veterans' Day. On the 11th hour of the 11th day of the 11th month of 1918, World War I (the then-most-ghastly-ever spree of killing technologies) officially ended, as per the armistice. This holiday salutes the fallen of WWI and other wars. The poppy has become its symbol ("poppy == war dead" goes back a further century), and they are sold, in fundraising drives. And resold to make heroin. No, not really.
As you read this, someone is dying in a war somewhere.