GMT
Greenwich Mean Time (GMT) originally referred to the mean solar time at the Royal Observatory in Greenwich, London, which later became adopted as a global time standard. It is for the most part the same as Coordinated Universal Time (UTC), and when this is viewed as a time zone, the name Greenwich Mean Time is especially used by bodies connected with the United Kingdom, such as the BBC World Service, the Royal Navy, the Met Office and others particularly in Arab countries, such as the Middle East Broadcasting Center and OSN. It is the term in common use in the United Kingdom and countries of the Commonwealth, including Australia, South Africa, India, Pakistan and Malaysia, and many other countries in the Eastern Hemisphere.
Before the introduction of UTC on 1 January 1972, Greenwich Mean Time (also known as Zulu time) was the same as Universal Time (UT), a standard astronomical concept used in many technical fields.