What does zulu mean on jag?

Coordinated Universal Time (UTC) and Zulu Time

Coordinated Universal Time functions as the primary international time standard by which the world regulates clocks and time. It is essentially the modern continuation of Greenwich Mean Time.

Within military communications, aviation, and meteorology, the United States Military designates this time zone as Zulu time. This nomenclature originates from the phonetic alphabet word assigned to the letter "Z," which represents the zero-meridian offset in the military time zone system.