standard time

noun

1. the time in any of the 24 time zones, each an hour apart, into which the earth is divided: it is based on distance east or west of Greenwich, England; the 8 zones of North America (Atlantic, Eastern, Central, Mountain, Pacific, Alaska, Hawaii-Aleutian, and Samoa) use the mean solar times of the 60th, 75th, 90th, 105th, 120th, 135th, 150th, and 165th meridians, respectively
2. the official time, whether mean solar time or daylight saving time, in any given region