its stands for greenwich mean time. Greenwich is named after Greenwich, England. It is where time mean time is 0. There are a lot of watches that represent and/ or have GMT inscribed on it. ie., the Rolex GMT
It is a type of watch that generates less than 3% gas. Quite cool, hey!
I also produces a speed reckignition which gose a fast speed of 90mph, now that is cool!
I woudn't reccommend them, cos they...