Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory in Greenwich, London. It is used as the basis for standard time throughout the world.
Universal Coordinated Time (UTC) is the primary time standard by which the world regulates clocks and time. It is based on International Atomic Time (TAI) with leap seconds added to keep it in sync with the Earth's rotation.
The main difference between GMT and UTC is that GMT is based on the Earth's rotation, while UTC is based on atomic time. This means that GMT may vary slightly due to changes in the Earth's rotation, while UTC remains constant.
Greenwich Mean Time is determined by the position of the sun in relation to the Prime Meridian, which runs through the Royal Observatory in Greenwich. This time is then used as the basis for all other time zones around the world.
UTC was created in order to have a standard time that was consistent and could be used globally. It was developed in response to the need for a more accurate and reliable timekeeping system, as well as the increasing importance of international communication and coordination.