GMT most commonly means Greenwich Mean Time , the standard time based on the prime meridian (0° longitude) at the Royal Observatory in Greenwich, London. In modern use, people also say “GMT” informally when they really mean the world reference time very close to Coordinated Universal Time (UTC).

Core meaning

  • Greenwich Mean Time is the mean solar time at the Greenwich meridian, historically used as the reference for all world time zones.
  • Other time zones are described as offsets from it, such as GMT+1 or GMT−5.

How GMT is used today

  • In everyday life, GMT is a convenient label for a fixed reference time, especially online for events, launches, or global meetings.
  • Technically, most official systems now use UTC, but many people still say “GMT” out of habit because it is widely understood.

Other contexts for “GMT”

  • In watchmaking, a GMT watch is a watch that shows local time and at least one additional time zone, using an extra 24‑hour hand.
  • In texting and internet slang, GMT can also mean “good morning text,” depending on context, especially in chats and social media.

How to know which meaning is intended

  • If you see “10:00 GMT” next to a date, it almost certainly refers to the time standard (Greenwich Mean Time).[
  • If it appears in casual messages like “send me a gmt,” it may be the slang “good morning text” instead.

TL;DR: “GMT” primarily means Greenwich Mean Time, the base reference for global time zones, but can also refer to dual-time watches and, in chats, “good morning text,” depending on where you see it.