Greenwich Mean Time
From Astrowiki-en
The time zone along the prime meridian which runs through Greenwich in England (the common abbreviated form for Greenwich Mean Time is GMT). It is identical with Universal Time UT) and sets the international standard for measuring time zones. For any kind of erected horoscope (in the case of a person the natal chart) all calculations are translated into Greenwich Mean Time. Planetary tables, so-called ephemerides are given according to GMT, either at midnight or midday.
