time zone

one of the twenty-four different regions on Earth determined by longitude and that determine one hour intervals in local time

A time zone is a region of the Earth that has adopted the same standard time, usually referred to as the local time. Most adjacent time zones are exactly one hour apart, and by convention compute their local time as an offset from UTC (see also Greenwich Mean Time). Standard time zones can be defined by geometrically subdividing the Earth's spheroid into 24 lunes (wedge-shaped sections), bordered by meridians each 15° of longitude apart. The local time in neighbouring zones would differ by one hour. However, political and geographical practicalities can result in irregularly-shaped zones that follow political boundaries or that change their time seasonally (as with daylight saving time), as well as being subject to occasional redefinition as political conditions change.
See more at Wikipedia.org...

One of approximately 24 longitudinal divisions of the globe, nominally 15 degrees wide, in which clocks show the same time. Some zones follow the boundaries of states or territories, others differ from neighbouring zones by more or less than one hour.
Computers can be programmed to take into account the time zone each user is working in, which is not necessarily the same as the zone the computer is in.
See also TZ.
(1997-07-20)

A geographic region within which the same standard time is used. (DOI4)

Noun
1. any of the 24 regions of the globe (loosely divided by longitude) throughout which the same standard time is used
(hypernym) zone, geographical zone