D-Day is a term often use in military parlance to denote the day on which a combat attack or operation is to be initiated. "D-Day" often represents a variable, designating the day upon which some significant event will occur or has occurred; see Military designation of days and hours for similar terms. The initial D in D-Day has had various meanings in the past, while more recently it has obtained the connotation of "Day" itself, thereby creating the phrase "Day-Day", or "Day of Days".