What do the letters in the GMT time zone stand for?

The letters in the GMT time zone stand for "Greenwich Mean Time." GMT is a time zone that was originally centered around the Royal Observatory in Greenwich, London, United Kingdom. It serves as a reference point for timekeeping and is often used as a standard for coordinating time globally. Greenwich Mean Time is based on the mean solar time at the Prime Meridian, which passes through the Royal Observatory in Greenwich. However, it's important to note that GMT is now largely replaced by Coordinated Universal Time (UTC), which is more precisely defined and is the basis for timekeeping worldwide. Despite this, the term GMT is still widely used and understood, especially in common language and historical contexts.