Main abbreviations you guys use please :)

[UltraWar]

---------------------------
AFK - Away from Keyboard
FTW - For the win
UW - UltraWar
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[Dutch_guy]

AAR
PBM (although I'm guessing it's something like "Player-based mod")
AoR

1. After Action Report.
   
2. Play by mail
   
3. Area of recruitment.

AFAIK = As Far As I Know.

FTW = For the win ?

[Martok]

FTW = For the win ?

Yes. FTW = For the win.

[Caius]

CF:Caius Flaminius

[Omanes Alexandrapolites]

I would link to a wiki page, but it contains bad langage, so I sadly cannot, or at least not without breaking the forum rules. Sorry. However, from what I know:

AFAIK — As far as I know
BTW — By the way
Bump — When somebody posts in a thread to bring it back up to the top of the forum page and get it noticed.
Spam — Posting, which often makes no sense, just to increase post-count. Most posts of this nature include the phrase "+1" to indicate the level of which their post count has increased by.
AoR (a.k.a ZoR) — Area/Zone of recruitment, A feature in many modifications, and in the games M:TW and R:TW, which restricts certain units to be trained in certain regions. For example, Swiss Pikemen can only be trained in the province of Switzerland or Spartan Hoplites only being available in Sparta and Syracuse.
PBM (a.k.a PBeM)— Play by (e-mail) campaign. A nice explanation of this can be found here.

Hope this helps, cheers!

[I Am Herenow]

Thanks guys! :)

Found two more confusing ones:

FRAPS
UI

Also, as for FTW ("for the win), "[x] ftw" means "[x] is (a) good (thing)". Could be extended to FTD, ~L (For the Draw, ~Loss) - again, "This is mediocre"/"This is bad", but those are really only joke ones.

[Warmaster Horus]

UI is User Interface, I believe. It's basically what you see on screen (Unit cards, mini-map...)
FRAPS, I don't think is an abreviation, but is a usefull program to take screenshots and videos. It's free, but in that case you can only get 30 seconds max videos. I don't know any other limitation.