‘D-Day’—which is military slang for the starting day of any operation—has come to mean the D-Day, the greatest amphibious invasion in history. It will be celebrated this year throughout the world and, most poignantly, on the five beaches of Normandy which bear the code names of Utah, Omaha, Gold, Juno, and Sword.
D-Day by Churchill biographer Martin Gilbert (Wiley, 2004) provides a fine overview of the entire event.