Definitions for "GREENWICH MEAN TIME"
Keywords:  gmt, utc, zulu, meridian, longitude
Since the prime meridian of 0 degrees longitude passes through Greenwich, England, this location is used for a universal time throughout the world. Each of the time zones are measured outward 15 degrees from the prime meridian. Thus, 1400 (2 PM) GMT is 0900 EST, 0800 CST, 0700 MST etc. GMT minus 7 hours equals MST. GMT is also called "Z" time and most NWS products, especially model guidance products, use this time.
n. The mean solar time at the prime meridian (0 degrees longitude) of Greenwich, England. Greenwich mean time is sometimes called Z time or Zulu time. Although Greenwich mean time and coordinated universal time are sometimes used interchangeably, they are not synonyms. Greenwich mean time is an approximate time. Because the second is no longer defined in terms of astronomical phenomena, the preferred name for this time scale is coordinated universal time (UTC).
Mean solar time for the meridian at Greenwich, England. Greenwich mean time is used as the basis for calculating time around the world. Greenwich time may also be referred to as Zulu or Z time.