Site Activity
Site Search(by Google)
I guess new players can simply get lost in the game when seeing so much strange expressions around them so let's summarize them all:

Game related:

Adds - unexpected reinforcements on enemy side when during fight
AFK - away from keybord (player is currently away from his computer)
Aggro - amount of aggresion monster has against player. Also used for describing radius around monster which is provoking its attack. Dealing damage to monster or healing other players in fight increases its aggro towards you. Creature generally attacks the character with most aggro.
Alt - your alternate character on your account (usually lower level than you main)
AoE - area of effect (describes skills or spells that affects all monsters in designated area)
AE - anti-exploit behavior of monsters
v#b#c# - volume, book, chapter(another example 1.12.9)
BoA - item that binds on acquire
BoE - item that binds on equip
BPE - Block/Parry/Evade
Buff - positive effect on monster or player (buffer is someone who use these effects on his friends); also used as opposite of nerf
Burg - burglar
CB - Controlled Burn, champion's legendary trait increasing damage and power regeneration
CC - crowd control (abilities and skills changing behavior of creatures - stun, root, mez, fear and other; CC class in this game is loremaster)
cd - skill cooldown, eg. "My hope pots are still on cd."
Champ - champion
CJ - conjuction, refers to fellowship maneuvres
CoD - cash on delivery (when using post service)
Craft/Crafting - term generally used for your secondary profession (apart from your class) which enables you to gather resources and make various things
Creeps - monsters (usually used in monster play; sometimes in PvE also)
Crit - Critical hit/success
Critter - non attacking creature
DC/dc'ed - disconnect/disconnected
Debuff - negative effect on monster or player; Debuffer is someone who use these effects on his enemies
Devs - developers, creators of the game
Ding - to level up
DoT - damage over time (skills and effects hurting enemies constantly during its duration)
DP - destiny points (used for temporary buffs in PvE or for buying skills and other thing in PvMP)
DPS - damage per second (damage skills/weapons/effects does to enemy in one second; also refers to classes with highest DPS - hunter, champion)
Drop - treasure you get from dead monster; synonymous with loot
EM - elite master mob
Freeps - free people (usually used in monster play)
FM - fellowship maneuvre, the same as CJ
FS - fellowship
GD - guardian
GG - good game/good group
GM - game master, game tech help you can call when you ran into some bug or other problem you can't solve other way; sometimes (in combination with a profession) it is used for describing grand-masters of craft specialization
Grinding - staying in the same area for very long time, harvesting resources or killing creatures to gain money, xp or items
GY - Grave Yard (spawn point where you appear after you get killed)
Healer - someone with ability to heal and resurrect other characters in battle (this is minstrel in LotRO)
HIPS - hide in plain sight, describing the burglar skill
HoT - healing over time (effect that heals target during its duration)
HS - Heartseeker, hunter's mega-nuke attack
IC - in character, describes someone who is in roleplaying state, see RP
ICMR - in-combat morale regen; how fast you regenerate morale during combat
ICPR - in-combat power regen; how fast you regenerate power during combat
IHW - In Harms Way, a captain skill that adds a small blue "light" icon which means the Captain has taken the damage that you took upon yourself
Instance - unique copy of area created for you or for your group
IRL - in real life, see RL
KB - killing blow
Kite - to kill monster from safe distance using ranged attacks and running whenever the enemy comes near. Two players working together may kite an enemy without actually moving with alternating attacks and creature running in good distance between them
LD - link dead, the same as DC
LFF - looking for fellowship, player needs fellowship for his quest; also a channel name
LFG - looking for group, the same as LFF
LFM - looking for more players to join existing fellowship
LFR - looking for raid to join
LM - abbreviation for Lore-master
LW - legendary weapons
LS - Last stand, 15 second captain's invulnerability
Loot - treasure you get from dead monster
LoS - line of sight
MA - main assist; character(s) assisting main tank with selected creature
Main - your main character on your account (usually the one with highest level)
Map (verb) - to use travelling skill to travel somewhere, eg. "I am going to map to..."
Mats - materials for crafting
Mez - a crowd control skill which temporary incapacitates target. Breaks upon the target taking damage; abbreviation of mesmerize
Meds - Medallions
Mini - minstrel
Mob - term used to describe computer controlled monster
MoM - Mines of Moria, first paid game expansion
MoT - Mark of Triumph
MP - monster play/monster player, see PvMP
MPS - morale per second
MT - main tank; the character who should generate the most aggro and hold creatures
Mule - character created just to store things
Nerf - game change when devs lower effeciency of some skill (players often whine because of it)
Newb(ie)/Noob - newbie is someone new to the game; noob is, on the other hand, player with low skill (some immature players use this term while swearing; other players find it offensive)
NPC - non-playing character; computer controlled characters
OMW - on my way, indicates that you are on the way to target location
OOC - out of character; sometimes used as "out of combat"
OOP - out of power; you write this when you are out of power and therefore can't use your skills
Off-tank, OT - usually just another tank in raids. His job is to run around and draw any mobs who escaped from main tank. He mainly chases mobs who escapes (or arrives) and are running after healer - he should take them back to main tank; OT si sometimes used as abbreviation for off-topic in chat (when you are talking about things from real life)
PC - player character; character you are playing
Pet - allied character creature/npc
Port - to transport yourself or/and others to some place in the world
Pot(s) - short for potions. These are consumables which give temporary buffs, like a hope bonus or fear removal
PPS - power per second
PST - please send tell, often used in expression "PST me", especially on Trade channel; player wants you to /tell [hisname] [text] him if you are interested
PUG - pick-up group; describes random group of people who doesn't know each other and got together to do some quest or raid
Pull - to draw monster from group; common strategy is pulling only one monster at time, so fellowship doesn't have to fight whole group
PvE - Player vs. Environment (type of play where players fight against computer controlled monsters or NPCs)
PvMP - Player vs. Monster Player (type of play where players fight monsters controlled by other players)
PvP - Player vs. Player (type of play where players fight against other players; in LotRO it equals PvMP)
Raid - group of players bigger then fellowship (up to 24 people) gathered to attack enemy. In raid, all player actions should be coordinated to win
RAT - raid assist target
Rep - reputation
Res/Rez - abbreviation of ressurect/ressurection; often used in sentence "Rez me, please" (some players, especially on RP servers, find this abbreviation offensive)
RK - runekeeper
RL - real life (outside the game)
Root - a crowd controll skill which renders a target incapable of moving from the spot but all other skills are available
RP - roleplay (alt. roleplaying/roleplayer) - type of playing when you act, write and behave as if you actually were your character; also used to identify servers specialized in this type of playing
Sig - signature mob
Stun - a crowd control skill which renders a target incapable of performing any action, even when being attacked
Tank - someone who gathers aggro of creatures to draw off the attention from other characters (guardian has this role in LotRO)
Taxi - funny name for hunters (mainly because of their travelling skills). Also used as verb. Some hunters finds this term offensive
Toon - alternative word used for player character
Train - a group of mobs fighting together; as a verb, train means "to flee ahead of monsters" usually due to misfortune but sometimes it is used as tactic to lead them away. Thus, the sentence "She is training the mobs" doesn't mean she's seeking to improve their skills but instead leading them for some sightseeing across the landscape.
Twink - character supported by higher-level character (by money, items etc.)
Vocation - set of three crafting professions
WD - Warden
Wipe/Wiped - sometimes, your whole group is killed in encounter - then you say you were wiped
WTB - want to buy
WTS - want to sell
XP - experience, refers to points you get for doing quests and fighting monsters

AH - Auction house
BG - Barad Gularan
CD - Carn Dum
DD - Dol Dinen
EL - Ered Luin
EM/EMS/Ettens - Ettenmoors
Foro - Forochel
GA - Garth Agarwen
GB - Great Barrows (often referring to southmost instance)
GF - Gath Forthnir
GS - Grand Stairs
GT - Goblin Town
Hele - Helegrod
HI - Haudh Iarchith, Bree reputation dungeon in Barrow Downs
IB - Imlad Balchorth
LL - Lonelands
MD - Michel Delving
MM - Misty mountains
ND - North Downs
OG - Ost Guruth
Rift - The Rift of Nûrz Ghâshu, level 50 12-man raid instance
RD/Riv - Rivendell
SH - Sword Halls
SG - Sammathy Gul
TB - Trestlebridge
TH - Thorin's Hall
TS - Trollshaws
Uru - Urugarth

Monster play: (Ettenmoors map)

BA - Blackarrow
CF - Coldfells
CP - Control Point, refers to conquerable location
CG - Captain General, used to refer to a boss in keeps.
DG - Dar Gazag
DF - Desperate Flight (much debated hunter's ability to run away from battle)
DoF - Delving of Fror, the same as Ettendeep
EC - Elf camp (site little south of Tol Ascarnen)
ED - Ettendeep (Delving of Frór, site bellow Ettenmoors)
GR - Grothum
HH - Hoarhallow (hobbit village)
HS - hotspot
Gank - this term is used when attacker(s) are way too stronger than defender(s) so they overrun them; also used when attacker attacks target fighting with NPC(s)
Goldie - Old Goldhead
Grams - Gramsfoot (creeps starter area)
GV - Glan Vraig (freeps starter area)
ID/Isen - Isendeep (northern mines)
LC - Lumber Camp (in Hithlad)
Lug - Lugazag
Moors - short for Ettenmoors
OC - Orc camp
OR/Ost - Ost Ringdyr
TA - Tol Ascarnen (contested isle in the center of map)
TR - Tirith Rhaw
WL - War Leader
x-roads - crossroads near EC

General: (non-game related/internet slang)

AFAIK - as far as I know
ASAP - as soon as possible
ATM - at the moment
Bump - a post whose purpose is to move the thread to the top of list again
bb - bye-bye
BRB/BBL - be right back/be back later
BRT - be right there
BTW - by the way
FPS - frames per second
GL - good luck
GJ - good job
Gratz/gz - congratulations
GTG - gotta go (if someone needs to leave); sometimes good to go
IIRC - if I remember correctly
IMHO - in my humble opinion
JK - just kidding
LOL - laughing out loud, acronym for something very funny (note that some immature players use this acronym way too much just to be cool)
nm - nevermind
nn - nighty-night
np - no problem
ofc - of course
OMG - oh my god!
OP - original poster
PM - private message
PPL - abbreviation for people
QFE - quoted for emphasis
QFT - quoted for truth
ROFL - rolling on the floor laughing, stronger expression for LOL, see there
THX - thanks
Troll/Trolling - someone who posts controversial and usually irrelevant or off-topic messages with the intention of baiting other users into an emotional response or to generally disrupt normal on-topic discussion
TY/TYVM - thank you/thank you very much
WB - abbreviation for welcome back
YW - you are welcome