This has all the abbreviations from A-M alphabetically. You'll find N-Z here. The categorized list is this way, or that way for class-specific abbreviations. Please leave comments on the main post.

1h: One-handed
2h: Two-handed
5SR: Five-second rule (the rule that mana regeneration from spirit only occurs if you haven't spent mana on a spell in the last five seconds)
AB: Arathi Basin [battleground]
AB: Arcane Brilliance/Arcane Blast [mage]
Add: An "additional" mob that has been aggroed, usually unintentionally
AE: Arcane Explosion [mage]
AFAIK: As far as I know [chat]
Aff/Afflic: Affliction talent tree [warlock]
AFK: Away from keyboard [chat]
Agg/Aggro: Probably short for "aggression" or some related word, it refers to who a mob is attacking -- that player is said to "have aggro" or have "pulled aggro"
AI: Arcane Intellect [mage]
Alt: An "alternate" character -- not your main character
AoE: Area of effect (a spell or effect that takes place over an area, as opposed to working only on a single target)
AotH: Aspect of the Hawk [hunter]
AotP: Aspect of the Pack [hunter]
AotV: Aspect of the Viper [hunter]
AotW: Aspect of the Wild [hunter]
AP: Arcane Power [mage]
AP: Attack power
AQ20/RAQ: Ruins of Ahn'Qiraj [raid]
AQ40/TAQ: Temple of Ahn'Qiraj [raid]
AR: Astral Recall [shaman]
Arm: Armory wing of Scarlet Monestary [instance]
AS: Arcane Shot [hunter]
ATM: At the moment [chat]
AV: Alterac Valley [battleground]
Ban: Banish [warlock]
BB: Booty Bay
BE/Belf: Blood Elf
BE: Blade's Edge [zone]
BF: Blade Flurry [rogue]
BF: Blood Furnace [instance]
BFD: Blackfathom Depths [instance]
BG: Battleground
Bio: Short for "biological," this refers to fulfilling biological needs (i.e. using the restroom); often used to explain AFKs in groups
BM: Beast Mastery talent tree [hunter]
BM: Black Morass [instance]
BoE: Bind on Equip
BoK: Blessing of Kings [paladin]
BoL: Blessing of Light [paladin]
BoM: Blessing of Might [paladin]
BoP: Bind on Pick-up
BoP: Blessing of Protection [paladin]
BoS: Blessing of Salvation [paladin]
BoU: Bind on Use
BoW: Blessing of Wisdom [paladin]
BRD: Blackrock Depths [instance]
BRS: Blackrock Spire [instance]
BRT: Be right there [chat]
BS: Backstab [rogue]
BS: Battle Shout/Battle Stance [warrior]
BS: Blacksmith/Blacksmithing
BT: Bloodthirst [warrior]
BTW: By the way
Buff: A beneficial spell, or a change to the game that makes a given class/spec stronger
BW: Bestial Wrath [hunter]
BWL: Blackwing Lair [raid]
Camo: Camouflage [rogue]
Cath: Cathedral wing of Scarlet Monestary [instance]
CB: Cold Blood [rogue]
CBA: Can't be arsed [chat]
CC: Crowd control
CloS: Cloak of Shadows [rogue]
CoA: Curse of Agony [warlock]
CoC: Cone of Cold [mage]
CoD: Curse of Doom [warlock]
CoE: Curse of the Elements [warlock]
CoEx: Curse of Exhaustion [warlock]
CoH: Circle of Healing [priest]
Conflag: Conflagrate [warlock]
CoR: Curse of Recklessness [warlock]
Corr: Corruption [warlock]
CoS: Curse of Shadows [warlock]
CoT: Curse of Tongues [warlock]
CoX: Curse of Exhaustion [warlock]
CoW: Curse of Weakness [warlock]
CS: Cheap Shot [rogue]
CS: Counterspell [mage]
Darn: Darnassus [zone]
DC: Death Coil [warlock]
Def: Defensive Stance [warrior]
Demo: Demonology talent tree [warlock]
Demo: Demoralizing Shout [warrior]
Dest/Destro: Destruction talent tree [warlock]
Deva: Devastate [warrior]
DI: Divine Intervention [paladin]
DIAF: Die in a fire [chat]
Disc: Discipline talent tree [priest]
DKP: Dragon Kill points, a cover term for a number of systems guilds use to distribute loot (see WoWWiki)
DL: Drain Life [warlock]
DM: Deadmines [instance]
DM: Dire Maul [instance]
DND: Do not disturb
DoT: Damage over time
DP: Dark Pact [warlock]
DPM: Damage per mana
DPS: Damage per second
DR: Damage reduction (due to armor)
DR: Diminishing returns
Drae: Draenei
DS: Defensive stance [warrior]
DS1/DS2/DS3: Class-specific "dungeon sets" of gear that drop from 5-man dungeons. DS1 and DS2 were known as Tier 0 and Tier 0.5, respectively, but that analogy breaks down when it comes to DS3.
DS: Divine Shield [paladin]
DS: Divine Spirit [priest]
DS: Drain Soul [warlock]
DW: Death Wish [warrior]
DW: Dual wield
Ele: Elemental talent tree [shaman]
Eng/Engi/Engy: Engineering
Enh: Enhancement talent tree [shaman]
EotS: Eye of the Storm [battleground]
EPL: Eastern Plaguelands [zone]
ES: Earth Shock [shaman]
Evis: Eviscerate [rogue]
Evo: Evocation [mage]
Exec: Execute [warrior]
Exo: Exodar [zone]
FA: First Aid
FB: Firebolt/Fire Blast/Frostbolt [mage]
FD: Feign Death [hunter]
FF: Faerie Fire [druid]
FFF: Faerie Fire (Feral) [druid]
FFS: For f---'s sake [chat]
FH/Fheal: Flash Heal [priest]
FoL: Flash of Light [paladin]
Fort: Power Word: Fortitude/Prayer of Fortitude [priest]
FP: Flight point/flight path
FR: Fire resistance
FS: Frost Shock [shaman]
FTL: For the loss (means "is bad") [chat]
FTW: For the win (means "is good") [chat]
FW: Fear Ward [priest]
Gads: Gadgetzan [zone]
GftT: Go for the Throat [hunter]
GG: Good game (often sarcastic) [forums]
GH/Gheal: Greater Heal [priest]
Gift: Gift of the Wild [druid]
GJ: Good job (often sarcastic) [forums]
Gnomer: Gnomeregan [instance]
GoA: Grace of Air totem [shaman]
GotW: Gift of the Wild [druid]
GTAoE: Ground-targeted AoE (an AoE spell for which the caster can choose a target, like Flamestrike)
GTFO: Get the f--- out [chat]
GW: Ghost Wolf [shaman]
GY: Graveyard wing [instance]
GZ: Gadgetzan [zone]
Hearth: Hearthstone
Hemo: Hemorrhage [rogue]
HF: Hellfire [warlock]
HF: Holy Fire [priest]
HFP: Hellfire Peninsula [zone]
HFR: Hellfire Ramparts [instance]
HH: Honor Hold [zone]
HL: Holy Light [paladin]
HM: Hunter's Mark [hunter]
HoJ: Hammer of Justice [paladin]
HoT: Heal over time
HoT: Howl of Terror [warlock]
HotW: Heart of the Wild [druid]
HoW: Hammer of Wrath [paladin]
HPM: Healing per mana
HPS: Healing per second
HS: Hearthstone
HS: Healthstone [warlock]
HS: Heroic Strike [warrior]
HT: Healing Touch [druid]
HW: Healing Wave [shaman]
IAotH: Improved Aspect of the Hawk [hunter]
IBTL: In before the lock [forums]
IDC: I don't care
IDK: I don't know
IDS: Improved Divine Spirit [priest]
IF: Inner Fire [priest]
IF: Ironforge [zone]
IIRC: If I recall correctly
Imba: Imbalanced; usually means "overpowered" [forums]
IMHO: In my humble opinion [chat]
Imm/Immo: Immolate [warlock]
IMO: In my opinion [chat]
Inc: Incoming [chat]
Incin: Incinerate [warlock]
Inn/Innerv: Innervate [druid]
IRL: In real life
ISS: Improved Sinister Strike [rogue]
Kara: Karazhan [raid]
Kings: Blessing of Kings [paladin]
KS: Kidney Shot [rogue]
KZ: Karazhan [raid]
L2P: Learn to play
LBRS: Lower Blackrock Spire [instance]
LF: Looking for ("LF tank," etc.) [chat]
LF1M/LF2M/etc.: Looking for one more, two more, etc. [chat]
LFG: Looking for group [chat]
LFM: Looking for more (for a group)[chat]
LHW: Lesser Healing Wave [shaman]
Lib: Library wing of Scarlet Monestary [instance]
Light: Blessing of Light [paladin]
Live Strat: Scarlet side of Stratholme [instance]
Lock: Warlock [warlock]
LoH: Lay on Hands [paladin]
LOM: Low on mana
LotP: Leader of the Pack [druid]
LS: Last Stand [warrior]
LT: Life Tap [warlock]
LW: Leatherworking
LW: Lightwell [priest]
MA: Main assist
MAP: Melee attack power
Mara: Mauradon [instance]
Mark: Mark of the Wild [druid]
Mats: Short for "materials;" refers to the ingredients in a crafted item
MB: Mind Blast [priest]
MC: Mind Control [priest]
MC: Molten Core [raid]
MD: Master Demonologist [warlock]
Medi: Meditation [priest]
MF: Mind Flay [priest]
Might: Blessing of Might [paladin]
ML: Master loot/master looter
MM: Marksmanship talent tree [hunter]
Mob: Short for "mobile" (derived from MUDs, where any NPC was either a stationary shopkeeper or mobile; see WoWWiki), this refers in WoW to NPCs, primarily NPCs that are meant to be killed.
MoD: Master of Deception [rogue]
MotW: Mark of the Wild [druid]
MP5: Mana per five seconds
MS: Master Summoner [warlock]
MS: Mortal Strike [warrior]
MT: Main tank
MT: Mistell (means "I sent this message to the wrong channel or person") [chat]

Continued here
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Tags: abbreviations, chat, netspeak, warcraft, world of warcraft, wow

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