AFK
Away From Keyboard.

Assist feature
Game command that lets you target the same mob the assisted player has targetted.

Autofollow
Command that automatically makes you follow other players (sticking).

Buffers
Classes that enhance their group mates with spells, commonly named buffs.

CH Rotation
Used in EverQuest 1 on the Main Tank. Three or more clerics would use Complete Heals timed after eachother, so that a CH would hit the MT every few seconds.

Crowd Control
How to deal with more than one mob (adds). Commonly used are off-tanking, mesmerizing and root parking.

Link Death
Connection loss of a player, booting him temporarily from the game.

Meat Shield
Another name for tanks.

Mezz
Short for mesmerize - rendering monsters inactive for a while. Especially useful if you're forced to attack several monsters at once, and want to take them one at a time.

Off Tanking
While the group fights a single target, a mob will be off-tanked by another melee class until the first mob is dead.

Raid Leader Channel
A chat channel created for the communication between vital players who lead the raid or assist the Raid Leader.

Spot-heal
Quickly cast heals which are used to prevent a player from dying after getting spike damage. Normally these are less mana-efficient.

Tank
A fighter archetype that gets and keeps the attention of the mob (aggro) to let other archetypes use their special skills.

Tank Order
List of the tanks. When the first on the list dies, number two takes over.