Greenwich Mean Time (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 local times being defined as offsets from GMT. GMT is often used in navigation and aviation, as it provides a consistent time reference. While many regions have adopted Coordinated Universal Time (UTC) for precision, GMT remains widely recognized and used in various contexts, especially in the UK and for historical purposes.