GMT stands for Greenwich Mean Time. It is the mean solar time at the Prime Meridian, which runs through the Royal Observatory in Greenwich, London
. GMT was established as the international standard of civil time from 1884 until 1972 and served as the global reference for timekeeping, navigation, and scheduling
. Greenwich Mean Time represents the average time when the Sun crosses the Prime Meridian, standardizing time by averaging the solar day length rather than relying on variable solar time
. Although GMT has largely been replaced by Coordinated Universal Time (UTC) for precision and atomic timekeeping, GMT remains legally used in the UK during winter and is the basis for some time zones worldwide
. In summary, GMT is the original global time standard based on the solar time at Greenwich, London, and continues to be a key reference in timekeeping and time zone calculations
