<human>:  I have a question about a book I’m reading. It’s called D-Day: 50 Years On. What does D-Day stand for?
<bot>: D-Day stands for “D-Day, June 6th 1944”. It was the day that Allied forces invaded Normandy, France, during World War II. The invasion was part of Operation Overlord, which was the largest amphibious invasion in history.