What was D day?

By far, the best known D-Day is June 6, 1944 — the day on which the Battle of Normandy began — commencing the Western Allied effort to liberate mainland Europe from Nazi occupation during World War II. However, many other invasions and operations had a designated D-Day, both before and after Operation Overlord. D-Day was originally planned for June 5, 1944 but bad weather and heavy seas delayed that.