The standard time zone for Greenwich Mean Time (GMT) is UTC+0. GMT is a timekeeping standard initially based on the mean solar time at the Prime Meridian, which runs through Greenwich, England. It was established in the 19th century and was widely used until the introduction of Coordinated Universal Time (UTC). GMT serves as a baseline for determining time zones around the world, where local times are defined in relation to GMT. Although many countries now use UTC for scientific and technical purposes, GMT remains an essential reference point in many contexts, especially for navigation and international communication.