Does anyone know what the "Z" stands for?

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.
1200z is
Melbourne Australia is in kilo time (10pm)
Halifax Canada is in tango time (8am)

daylight savings does not effect zulu time

Thank you for explaining.