There are lots of special terms every Garry's Modder should know and here are some of the ones I know:
Addon: Any DLC (downloadable content) for Garry's Mod.
Admin: Short for Administrator. A rank for players who are trusted by the owner of a server and have been given the ability to be the police of the server.
Ban: A severe punishment on servers which bars you from them for a set amount of time.
Console: A menu which allows players to enter special commands. It is activated by pressing the ~ button.
Dupe (Noun): Short for duplication. Any creation loaded with or saved with the Advanced Duplicator tool which lets players save their creations.
- (Verb): To make a copy of a creation using the Advanced Duplicator or the standard Duplicator tools.
FPS: Stands for Frames Per Second. This is the frame-rate of your computer while running a game or video. When it slows down it is called "Lag"
God (Noun): Also called godmode. If a player has godmode they cannot be killed conventionally except by console or admin commands.
- (Verb): To give someone godemode.
Griefing: Insulting other players or doing things to them because you are mad.
Kick: To remove someone forcibly from a server. Players who are kicked can rejoin right away if they want.
LUA: The programming language that addons for gmod are written in.
Lag (Noun): The result of computational overload on a server. Can be coused by spamming, too many props, too many players, and some contraption
- (Verb): Doing anything that causes the server to lag, whether intentional or not.
Minge (Noun): Any player that destroys other players creations without the other party's consent using their own weopons or creations.
- (Verb): Destroying other player's creations using your own weapons or creations.
Moderator: Sometimes called mods. They are one rank bellow Admin and are in training for Admin.
Noclip: Allows players to fly and pass through anything unless blocked by the server owner. Default toggle button is v.
RDM: Random Death Matching. This is randomly killing other players for no reason using your guns.
RP: Stands for Role Playing. Usually used to describe a server with a roleplaying game mode.
Spamming: Doing anything repeatedly that lags the server or annoys people.
- Prop spamming: Spawning one or more props reapeatedly, usually large ones, to purposely crash a server.
- Chat spamming: Typing too much in chat purposely so it is harder for other people to read there messages to each other.
- Mic spamming: Over using the microphone purposely to annoy people and make it hard for others to communicate.
Squeaker: Anyone who makes loud high-pitch sounds over the microphone to annoy other players.
Squeaking: Making loud high-pitched sounds over the microphone to annoy other players.
STool: Stands for Scripted Tool. These are tools that can be obtained in addons for gmod.
Spray: An image that can be "sprayed" on surfaces by players.
SWep: Stands for Scrited Weapon. Any weapon that can be obtained in an addon that is not standard for gmod.
TTT: Trouble in Terrorist Town. This is a game mode that some servers run. I don't know much about it.
Permaban: The most severe punishment on a server. A player is barred from the server forever.
Ping: A number that shows up next to your name in the player list. The higher it is, the worse your connection is to the server. The lower it is, the better.
Prop Surfing: Using the physgun to lift a prop you are standing on in order to "surf" on it.
Prop Pushing: Using the physgun to push your props on other players or their creations.