What is "GMT" commonly known as?

"GMT" commonly stands for Greenwich Mean Time, which is a time standard that was originally established based on the mean solar time at the Royal Observatory in Greenwich, London. GMT serves as a reference point for time zones worldwide and is often used in navigation, aviation, and various international relations where synchronization of time is essential.

Greenwich Mean Time has historical significance as it was once the standard for timekeeping across the world. Although it has largely been replaced by Coordinated Universal Time (UTC) for many purposes, GMT remains widely recognized and used, especially in contexts that require precise timing, such as scheduling in international communications and transportation.

The other choices provided refer to terms that are not recognized as standard definitions or do not have significance in the context of timekeeping in the same way that GMT does. This highlights the unique role that Greenwich Mean Time holds in various global contexts.