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**From Wikipedia,

Battle plans for the Normandy Invasion, the most famous D-Day.D-Day is a term often used in military parlance to denote the day on which a combat attack or operation is to be initiated. "D-Day" often represents a variable, designating the day upon which some significant event will occur or has occurred; see Military designation of days and hours for similar terms. The initial D in D-Day has had various meanings in the past, while more recently it has obtained the connotation of "Day" itself, thereby creating the phrase "Day-Day", or "Day of Days".[1] On the same principle, the equivalent terms in French, Basque, Romanian and Slovenian are Jour J, E eguna, Ziua-Z, and Dan D.[citation needed]

The best known D-Day is June 6, 1944 — the day of the Normandy landings — initiating the Western Allied effort to liberate mainland Europe from Nazi occupation during World War II. **