Greenwich Mean Time, or GMT, is a time standard that was established in the 19th century. It is based on the mean solar time at the Royal Observatory in Greenwich, London. GMT serves as a reference point for time zones around the world, with many regions using it as a baseline to calculate their local time. GMT is often used in navigation and aviation, as it provides a consistent time reference regardless of location. While many places have adopted Coordinated Universal Time (UTC) as a more precise standard, GMT remains widely recognized and is still used in various contexts, especially in the UK.