GM is the abbreviation for a car company.
However, In the world of Dungeon's and Dragon's it's an abbreviation for Game Master (get it GM)... Yeah I was one of those kids, who dabbled in the odd RPG (roll playing game) with friends... I'd watched a great little documentary over on HULU, about people that were game masters, and what they're lives were like since they loved D&D so much... IT was pretty interesting, a little depressing too, and made me pretty nostalgic for gaming with friends... SO Here's a grumply little goblin type dude with a torch shouting at some of his gamers.... THACO!!!! Critical HIT!!!! ROLL A D6!!!!
Hope you dig.