SB = Shining Balad, one of Vincent Rio's buffs
3S = Added after a wep name, indicates item has 3 sockets (same for 1S and 2S)
SC = Soul Crystal
CM = Castilla Mine
CR = Castilla Ruins
MCC = Multi-Character Control, the fancy way of saying 'control 3 chars at once'
MCC1 = Indicates you can only use one character, or only have 1 in your team.
AMs = Refers to AM's Boost, a potion buff.
KTV = Katovic Snowfield
SST = Server Standard Time
Inv = Invite, most often in reference to a squad.
PM = Private message
AC = Armor Crasher
BB = Black Bishop - a e100 LoE
LoE = 'Lord of Elements', a specific type of bracelet, has no official element affiliation
GS = Greatsword, a two-handed melee weapon
2H = A two-handed melee weapon (ie: Greatswords)
1H = A one-handed melee weapon, specifically Swords.
Edit: Dangit Flocky, you beat me to some of these xD
Repeats of mine, but with some other info:
LTA = La Tierra del Amor - Now labled as 'Tierra de la sed'
FF = As in 'FF Buff' is the Faction Fight (Buff) avaliable outside Auch at 18:00 Server Time