GMT is Greenwich Mean Time: the time of day as measured at Greenwich, in London, used for many years as the world’s shared baseline for clocks. When people say a country is ‘GMT+8’, they mean its clocks are eight hours ahead of that London baseline — Taiwan is GMT+8. Airlines, radio, and old-fashioned world maps still talk in GMT, and British winter time is GMT. Though actually, scientists now keep the official world time with atomic clocks, under the name UTC, and for ordinary life UTC and GMT stay in step. You will still hear GMT in news and travel, and it is the name learners meet first. Greenwich is a real place on the River Thames; the old observatory there is why this London suburb became ‘the zero line’ for time. GMT is not a time zone you ‘join’ in Taiwan. It is the reference other zones are counted from.