Greenwich Mean Time (GMT) is the solar based time in Greenwich, England, on which time in all other time zones in the world is based.
Greenwich Mean Time (GMT) is a time standard that is used as a reference for timekeeping in the travel, transport, and hotel context. GMT is the time at the Prime Meridian, which is the line of longitude that passes through the Royal Observatory in Greenwich, London, England. GMT is often used as a reference time for scheduling flights, trains, and other transportation services, as well as for coordinating events and activities in the travel and hospitality industry.
For example, a flight departing from New York at 8:00 AM Eastern Daylight Time (EDT) would be scheduled to depart at 12:00 PM GMT. Similarly, a hotel might list its check-in and check-out times in GMT, so that guests from different time zones can easily understand the hotel's schedule.
It's worth noting that, the use of GMT is not widely used currently as it has been replaced by Coordinated Universal Time (UTC) as the international time standard. UTC is the time standard used by most of the world, it's based on atomic clocks and it's kept constant by leap seconds.
It's common that in the travel and transportation industries, they use UTC instead of GMT as a reference time.