For people new to the game it's often hard to understand what people are saying.
Therefor this Dictionary of WOW "slang".
Some words have different ways of saying them i.e. "n00b" examples of that will be posted like this:
n00b: Newbie (nub - naab - newb - noob)

Feel free to reply things I forgot.


Basics

Addon: A patch you add to the game
AFAIK: As Far As I Know
AFK: Away From Keyboard
BRB: Be Right Back
CBA: Can't Be Asked
CC: Crowd Controll
DPS: Damage Per Second
FP: Flight Path
FTW: For The Win
GM: Game Master / Guild Master
GTFO: Get The F*ck Out
Gief: Give me
GZ: Congratulations (Gratz)
HPS: Healing Per Second
IDD: Indeed
IMO: In My Opinion
IMHO: In my honest opinion.
KK: ok (K)
L2: Learn to
L2P: Learn to Play
LF: Looking For
LFG: Looking For Group
LFM: Looking For Members / Looking For More
LOL: Laugh Out Loud (kek)
Mod: Modification to your interface
MP5: Mana (regenerated) Per 5 seconds
N00B: Newbie (nub - naab - newb - noob)
NOPE: No (nopz - nah - nty)
NP: No Problem
OMG: Oh My God (OMFG)
OP: Over Powered
PLZ: Please (plx)
Premades: A raid or group made prior to the battle.
PUG: Pick Up Group
RDY: Ready (R - RD)
Regen: Regeneration
Rest: Restore health/mana/energy
ROFL: Rolling On the Floor Laughing
STFU: Shut The F*ck Up
TBH: To Be Honest
TPS: Threath Per Second
TY: Thank You (thnx)
WTB: Want To Buy
WTC: Want To Craft
WTF: What The F*ck
WTS: Want To Sell
WTT: Want To Trade
Y: Yes (yeh - aye - yargh)
YW: You're Welcome
Zep: Zeppelin




Forum slang

Blue: a Blizzard Moderator
CM: Community manager
Dev: developer
Epeen: Internet Ego http://www.urbandictionary.com/define.php?term=e-peen
Flaming: Insulting or downtalking http://www.urbandictionary.com/define.php?term=Flaming
IBTL: In Before The Lock
L33t: Elite http://www.urbandictionary.com/define.php?term=l33t
OP: Original Post(er) / Opening Post(er)
Owning: Defeating someone in a noticible way (Pawn - pwn - p00nt - ownt) http://www.urbandictionary.com/define.php?term=Own
QFT: Quoted For Thruth
QQ: A crying Smiley
Spec: Specification of talent points.
Sticky: a post that is set to stay on top of the post list.
Trolling: Making fun of someone else http://www.urbandictionary.com/define.php?term=trolling
W00T: A cheer used in different circumstances. (wewt - woot - wuut)


Guild related

CL: Class Leader
CM: Class Master
DKP: Dragon Kill Points
Endgame: The final challange
GM: Guild Master
GMOTD: Guild Message Of The Day (MOTD)
Ginfo: Guild Info
Prio: Priority
PVE: Player Versus Enviorment
PVP: Player Versus Player


Races/Classes

Backstabber: Rogue
Belf: Blood Elf
Corpse: Undead (scourge - zombie - undude - boner)
Cow: Tauren
Dorc: Orc
Dorf: Dwarf (d00rf - dorf)
Dr00d: Druid (drewd)
Huntard: Hunter
Lolladin: Paladin (Pally - skilladin)
Nelf: Night Elf (nubelf - nerf)
Shammy: Shaman
Warlol: Warlock (Lock - skillock - warc*ck)
Warr: Warrior




Instances

1-60
AQ20: Ruins of Ahn'Qiraj
AQ40: Temple of Ahn'Qiraj
BFD: Blackfathom Deeps
BRD: Blackrock Depts
BWL: Blackwing Lair
DM: Deadmines
DiM: Dire Maul ( Often said as DM )
Gnomer: Gnomeregan
LBRS: Lower Blackrock Spire
MC: Molten Core
Naxx: Naxxramas
Ony: Onyxia's Lair
RFC: Ragefire Chasm
RFD: Razorfen Downs
RFK: Razorfen Kraul
SFK: Shadowfang Keep
SM: Scarlett Monestary
ST: Sunken Temple
Scholo: Scholomance
Stocks: Stockades
Stratt: Stratholme
UBRS: Upper Blackrock Spire
WC: Wailing Caverns
ZF: Zul'Farrak
ZG: Zul'Gurub



Battlegrounds

AB: Arathi Basin
AV: Alterac Valley
EotS: Eye of the Storm
WSG: Warsong Gulch



Zones and Cities

EPL: Eastern Plaguelands
IF: Ironforge
OG: Orgrimmar ( Org )
STV: Stranglethorn Vale
SW: Stormwind
TB: Thunder Bluff
TM: Tarren Mill
UC: Undercity
WPL: Western Plaguelands
XR: Crossroads ( Xroads )

This is a nice idea - we have a list of acronyms on the website, but it's good to have one in the forum too so I'll add this to the Newcomer reading sticky:
Helpful Newcomer Reading

I have seen people asking what DPS, HPS and TPS mean before so it might be good to add those into your list, although Healing per Second and Threat per Second are rarely used outside of endgame raiding.