While browsing the official forums, the Epic Character Build Guild forums or other Neverwinter nights websites you'll see a lot of abbreviations like NWN, HotU, CEP, HLA etc. I'll try to make a list here of most abbreviations and their meanings and add a link if applicable

Also have a look at the List of Acronyms at the NWNWiki

A	(top)
AA	Arcane Archer	Prestige class
AB	Attack Bonus	Game mechanic
AC	Armor Class	Game mechanic
AME	Academy for Modding Excellence	Guild
B	(top)
BAB	Base attack bonus	Game mechanic
BBoD	Black blade of disaster	Spell
C	(top)
CEP	Community Expansion Pack	Expansion
Cha	Charisma	Ability
Con	Constitution	Ability
CoT	Champion of Thorm	Prestige class
CR	Challenge Rating	Game mechanic
D	(top)
DC	Difficulty Class	Game mechanic
Dex	Dexterity	Ability
DM	Dungeon Master	Game mechanic
DP	Divine Power	Spell
DR	Damage reduction	Game mechanic
DW	Dual Wielding	Game mechanic Feat
DwD	Dwarven Defender	Prestige class
E	(top)
EDR	Epic damage reduction	Feat
ESF	Epic skill focus	Feat
	Epic spell focus	Feat
EWF	Epic weapon focus	Feat
EWS	Epic weapon specialization	Feat
F	(top)
FE	?
Fort	Fortitude	Game mechanic
Ftr	Fighter	Class
G	(top)
GMW	Greater magic weapon	Spell
GP	Gold pieces	Game mechanic
H	(top)
HCR	?
HD	Hit dice	Game mechanic
HiPs	Hide in Plain Sight	Feat
HPs	Hit points	Game mechanic
HS	Harper Scout	Prestige class
HLA	High level ability
HotU	Hordes of the Underdark	Module
I	(top)
Int	Intelligence	Ability
L	(top)
LoS	?
M	(top)
MP	Multiplayer	Game type
MS	Move silently	Skill
N	(top)
NPC	Non playable character	Game mechanic
NWN	Neverwinter Nights	Module
O	(top)
OC	Official campaign	Module
P	(top)
PA	Power attack	Feat
PC	Playable character
PGC	Pretty good character creator/converter	Tool
PM	Pale Master	Prestige class
PnP	Pen and Paper
PRC	Player Resource Consortium	Guild
PvM	Player versus Monster	Game type
PvP	Player versus Player	Game type
PW	Persistent World	Game type
R	(top)
RDD	Red dragon disciple	Prestige class
Refl	Reflex	Game mechanic
RP	Roleplay	Game type
S	(top)
SD	Shadow Dancer	Prestige Class
SoU	Shadows of Undrentide	Module
SP	Singleplayer	Game type
Str	Strength	Ability
T	(top)
TS	True seeing	Spell
TWF	Two weapon fighting	Feat
U	(top)
UMD	Use magic device	Skill
W	(top)
Wis	Wisdom	Ability
WF	Weapon Focus	Feat
WM	Weapon master	Prestige class
WS	Weapon specialisation	Feat
X	(top)
XP	Experience points	Game mechanic