Lets think back to my geography lesson... Well means Greenwich Mean Time, the local time at the 0 meridian (0 Degrees Latitude, the lines you see on the globe or maps etc). and it passes through Greenwich, England. Three English scientists made it up so the times are the same all around the world and they can relate back to the GMT. Basically if its 4:00pm in england you plus the time to it in your country (Depending on Daylight savings). Yeah basically load of tosh bullshit to me...