time zone One of 24 divisions of the Earth's surface, each 15° of longitude wide, within which the time of day is reckoned to be the same. At a conference held in Washington, D.C., in 1884, the meridian of Greenwich was adopted as the zero of longitude, and zones of longitude were established. Standard time in each successive zone westwards is one hour behind that in the preceding zone. See also Greenwich Mean Time (GMT)

time zone • n. see zone (sense 1).