1. Short for Game Masters, GM's are real people who help run, maintain, and assist other players in online games.
2. Short for Gold Master or Golden Master, GM is a master copy of software that is released after testing and used for all future copies. For example, when Apple releases their MacOS operating system or other software applications they first release their GM for reproduction. Microsoft refers to this as RTM.
3. Shorthand for Good Morning, GM is often used in chat rooms to greet users in the morning.
4. GM can also be short for Good Manners and is sometimes used in computer games and chat rooms.