AFK - Away From Keyboard. A player might enter a map and then leave computer running without exiting. Even if your not blocking anyone, it's not a good idea to be AFK for longer than a minute or two as another player might be trying to get into the map and you are taking up a slot. Sometimes admins will manually or automatically kick you off the server if you are AFK for a certain time.

CNC - Map names starting with "Cnc_" are based on Command & Conquer style game. You play as a commando mission. Usually an objective must be achieved within a timelimit.

Creepsworld - A popular fan website that is no longer online. You probably heard of them in connection with the "Creepsworld Top 50" which would be their fans choices for the best (At that time) 50 Sven Co-op maps .The site had much participation from the Sven Co-op community. Here's a list of some review scores done by them. I've found some of their reviews and pages on the Internet Archive Wayback Machine.

Blocker - A player who purposely blocks out other players (usually in vent entrances and exits or in small entranceways). This is usually done to distrupt the game and tick you off. If an admin is present the blocker can be kicked or banned from the map. If not, you can start a vote to kick the player. Some have suggested that new versions of Half-life and/or Sven Co-op provide an anti-blocker key whereas if a blocker won't move, you press a key to pass through him.

CVAR - Configuration Variable

Entmap - is a plugin that allows to change an add entities (objects) into a map. Fun if you like to build stuff with others. There are servers out there that only run entmaps

FUBAR - Military lingo. F**ked Up Beyond All Recognition

Lamer - When you are being called a lamer it means that someone is complaining about they way you are playing. Maybe you're blocking other player, or using some unfair tactics . Other acts of lameage: swearing, excessive voice or text commenting, racial jokes, or general bad behavior.

Latency - The amount of time it takes for a packet of information to travel from the source (usually the server) to you. The lower the latency the quicker/better. i.e. the speed you are connected to the source at.

WON - World Oppenent Network. It's a system that was introduced by Sierra and primarily used for Half-Life, though other games did use it.

wOOt - An expression use to signifiy happiness or elation. Usually over the internet.