z = Zulu
military/air transport/sea transport representation of Greenwich Mean time, or, Coordinated universal time
the globe is divided into 24 time zones a-x instead of 3 hours ahead or 4 hours behind, the zero line is labelled zulu (phonetic z) to distinguish it. times ending in z are universal times that can be converted easily(?) to local time, regardless of where local is.
Melbourne Australia is in kilo time (10pm)
Halifax Canada is in tango time (8am)