Which statement best describes Julian date?

Julian date refers specifically to the method of representing the day of the year. This system assigns a number to each day of the year, starting with 1 for January 1 and ending with 365 (or 366 in a leap year) for December 31. This format is particularly useful in environments like scientific research, astronomy, and military operations where clarity regarding the day of the year is important.

In the context of the choices provided, the other statements do not accurately define the Julian date. While policy dates and fiscal years are important aspects of calendar management, they do not relate directly to the Julian date system. Furthermore, lunar phases pertain to a completely different aspect of timekeeping and do not correspond with the Julian date format. Thus, stating that Julian date represents the day of the year accurately encapsulates its definition and use.