Someone stepping in
NWN - Neverwinter Nights, used for The Original Game as well as for The Game.
SoU - Shadows of Undrentide, the first expansion pack.
HotU - Hordes of the Underdark, the second expansion pack.
CEP - Community Expansion Pack, a compilation of a lot of custom content into a single hack pack.
EfU - Escape from Undermountain, Ziroc's module.
Incidentally, CEP works with all versions of NWN.