What is d-day and what does it stand for?

The "Order of the Day" memo that you have quoted was General Eisenhower's statement to the armed forces who were about to participate in the D-Day landing in Europe in June, 1944.

As reported by the National Archives (where a copy of Eisenhower's document is posted):

This order was issued by Gen. Dwight D. Eisenhower to encourage Allied soldiers taking part in the D-day invasion of June 6, 1944. Almost immediately after France fell to the Nazis in 1940, the Allies planned a cross-Channel assault on the German occupying forces, ultimately code-named Operation Overlord. ...  His printed Order of the Day for June 6, 1944 ... was distributed to the 175,000-member expeditionary force on the eve of the invasion.

africa

explanation:

benito

: ) hava a nice day