1. 6th June, 1944, the day on which the British, US, and other armies arrived on the beaches of northern France in the Second World War
2. the day when something important happens, usually something that you have been planning for a long time
Origin and usage
The term D-Day was first used towards the end of World War I, in 1918. It comes from military jargon: D-Day refers to the day on which an operation is due to start, and H-Hour the time. The reason for using the terms is either to preserve secrecy about the date and time of an attack, or because they have not yet been definitively decided.
Although D-Day has been used to refer to many different military operations, it is most commonly used to refer to the Allied landings on the coast of Northern France on 6th June 1944. The landings were originally intended to take place the previous day but were delayed because of bad weather. The invasion was codenamed Operation Neptune, but the term D-Day caught on and has been used ever since. This year marks the 75th anniversary of D-Day, and the event is being commemorated with more ceremony than usual. Veterans of the operation, all at least in their 90s, have gathered to remember their own part in the events and to commemorate their fallen comrades: casualties on both sides were very high, with over 4,400 Allied soldiers losing their lives and similar losses on the German side. D-Day is also used informally to refer to any important event, especially one that has been planned for a long time.
“Over a dozen world leaders gathered in the south of England on Wednesday to commemorate the 75th anniversary of D–Day.
“The idea of a potluck blossomed and after a week of planning and coordination D-Day arrived and voila! I am sitting and writing this blog with a full tummy and a satisfied grin.”
Allied, the Allies, beachhead, landing craft, Normandy Landings