-In pvp (and some general)

J / JJ / jjjjjjjjjj = whatever. It's all 'join'
Rj = ready to join (same as' stand by')
Rg = re-group
Jb = join block
Nb = no button
F = full (same as nb)
Vs = versus (This is not a verb, but usually used as a verb for 1vs1 fight.)
Gf = good fight (usually used after each fair match or vs)
Mid = middle of ctf map (for a fair game)
DC = disconnected
Aa = arcane ability of pets.
Cd = cool down of aa or skill

-Chat
Gc = guildchat
Oc = officer chat
Pm = personal message

-Skills
Warrior
Ss = skyward smash
Cs = chest splitter
Wm = windmill
At = Axe throw
Rc = rally cry
Jg/jug/jugg = juggernaut
Vg = vengeful blood
Hor = horn of renew

Rogue
Sp = shadow piercer
Nox = noxious bolt
As = aimed shot
Sss = shadow storm shot

Mage
Fb = fireball
Ib = frost bolt (I see many people call it this way. I think they meant 'iceball')

-Others
Lb = leaderboard

These are all I can think up atm
Hope this help for new players