"D-데이" refers to a specific day on which a significant event is scheduled to occur. The term is often used in military contexts to denote the day an operation is set to begin, such as the D-Day during World War II, when Allied forces landed in Normandy on June 6, 1944. It can also apply to various other events, including project launches or product releases. In modern usage, "D-데이" has expanded to include countdowns for personal milestones, such as weddings or exams. People often use it to mark the days leading up to these important occasions, creating excitement and anticipation for what is to come.