Zero Hour' is a term used to refer to a specific moment in time when a critical event or decision must take place. It is often used in military contexts, such as the D-Day landings during World War II, when Allied forces launched their invasion of Normandy on June 6th, 1944. The term 'Zero Hour' can also be used to refer to a DEADLINE or JUNCTURE, when a decision must be made or a task must be completed. It can also refer to a crossroads, where multiple possibilities exist and a choice must be made.