Grinding
Repeating a task over and over to achieve a goal. Generally refers to something that takes a long time, such as gaining experience, faction reputation, skill points, or honor.
Griefer
A person who purposely tries to annoy or anger other players.
Green
Uncommon level items. The lowest quality of items that can be disenchanted and the most common type of enchanted gear. Better than whites or grays, worse than blues and purples.
Gnomer
Gnomeregan, an instance in Dun Morogh
GM
Game Master. Someone employed by Blizzard Entertainment to assist and help players. Also can mean Guild Master. Also refers to Gold Mine, a node captured in Arathi Basin.
GCD
Global Cool Down. Activating most abilities or spells causes this to begin, blocking the player from using any spell for between 1 and 1.5 seconds
Gank
A term used when a player kills another player who has little or no chance to win, such as while already engaged in combat.
FTW
For The Win, used to express approval of a player, ability, strategy, or anything else.
FTL
For The Loss, used to express disapproval of a player, ability, strategy, or anything else.
Farm
Content that doesn't pose a high amount of challenge. Can refer to many things from gathering materials to repeating a raid encounter that has been defeated many times.