( in full Greenwich Mean Time )
the time of day on the line of 0° longitude (= a straight line between the North Pole and the South Pole), which goes through Greenwich (also called the Greenwich Meridian Line). It is the official time in Britain from October to March. Different time zones in other parts of the world are usually described with reference to GMT:
New York is five hours behind GMT so it’s early morning there now
Compare British Summer Time . See also Royal Observatory .