There's been a thread with a lot of useful abbreviations, I don't have the link though

- edit - emu'd
- edit2 - Added all the ones of that 'list' and added many more.
just to kick off:
EU:3 Lingo (Europa Universalis:3)
AAR = After Action Report
ADM = Administrative rating of a ruler
AE = Administrative Efficiency
ART,
arty = Artillery
BB = Badboy
CAV = Cavalry
CB = Casus Belli
CoA = Coat of Arms
CoT = Centre of Trade
DEF = Defensiveness (fort defensiveness specifically), or 'defense', or 'definitely'
DIP = Diplomatic rating of a ruler
disc = Discipline
DoW = Declaration of War (usually used in the sence of 'attack' or 'invade')
GC = Grand Campaign
HYW = Hundred Years War
INF = Infantry
MIL = Military rating of a ruler
NI = National Idea
OPM = One Province Minor (
2PM = 2 Province Minor)
PE,
PE% = Production Efficiency (percentage)
PTI = Permanent Terra Incognita
PU = Personal Union
RM = Royal Marriage
RR,
RR% = Revolt Risk (percentage)
stab = stability
stab hit = losing a stab level
stab hitting = lowering someone elses stab lvl (usually by them refusing a good peace deal)
TE,
TE% = Trade Efficiency (percentage)
TI = Terra Incognita
WC = War Capacity, or World Conquest
WE = War Exhaustion
WP = White Peace
WS = War Score
National Ideas: (NI's)
QFTNW = Quest for the New World
DV = Deus Vult!
LEF = Liberté, égalité, fraternité
SR = Scientific Revolution
SE = Smithian Economics
Country related:
BBB = Big Blue Blob (France)
BWB = Big White Blob (Austria)
HRE = Holy Roman Empire
OE = Ottoman Empire
Tags:
CAS = Castille
HAB = Austria (Habsburg Austria)
NAT = Natives (Special tag)
PIR = Pirates (Special tag)
REB = Rebel Scum (Special tag)
TUR = Ottoman Empire
Generic Game Lingo
AI = Artificial Intelligence (the computer)
CTD = Crash To Desktop
def = Defense, or 'definitely', or 'defensiveness' (EU:3 fort defensiveness specifically)
dmg = damage
FoW = Fog of War (Unable to see detailed information like troop movements in areas where you don't have a presence)
gfx = graphics
mod = modification
mp = multiplayer, or manpower
RTFM = Read The F**king Manual
tac = tactic
UI = User Interface
Game Versions
vanilla = unmodified version of the game (unflavoured, as it came out of the box) Sometimes refers stricly to version 1.0, sometimes to any version before the first expansion (Napoleons Ambition) and sometimes to any version without user-modifications.
NA = Napoleon's Ambition, the first expansion pack
IN = In Nomine, the second expansion pack (requires the first one)
HttT = Heir to the Throne, the third expansion pack (requires either both NA and IN, or EU:3 complete)
complete = EU:3 complete, the 'gold edition': EU:3 with its two expansion packs incorporated
HoI = Hearts of Iron (the 1st version, or any version depending on the user)
HoI2 = Hearts of Iron 2
HoI3 = Hearts of Iron 3
Vicky or
V1= Victoria (1)
V2 = Victoria 2
Ricky = 'Revolutions' expansion pack for Victoria (1)
EU:R = Europa Universalis: Rome
VV = 'Vae Victis', expansion pack for EU:R
CK = Crusader Kings
EU2 = Europa Universalis 2
Dip = Diplomacy
CE = Collector's Edition
Mods:
MM = Magna Mundi
MMP = Magna Mundi Platinum (current version, for others check the Magna Mundi subforum)
MEIOU = ...
WWM = Whole World Mod
TOT = Theatrum Orbis Terrarum
SRI =
Sacra Romanum Imperium
Forum Lingo
AFAIK = As far as I know
ASAP = As soon as possible
CP = Control Panel (The place to change your forum settings, profile, avatar, etc.)
def = Definitely, 'defense', or 'defensiveness' (EU:3 fort defensiveness specifically)
FAQ = Frequently Asked Questions
FUBAR = F***** up beyond all [repair, recognition, redemption, etc.]
FYI = For your information
gf = Girlfriend
GG = Gamersgate (Paradox' own online game shop) or good game (often used sarcastically)
IDK = I don't know
IIRC = If I recall correctly
IMHO = In my humble opinion
IMO = In my opinion
lmao = Laughing my ass off
lol = Laughing out loud
OMG = Oh my God
OP = Original Poster
OT = Off-topic
OTOH = On the other hand
thx = Thanks
ty = Thank you
WAD = Working as designed
WTF = What the F***
WTH = What the Hell
yw = You're welcome