Here are some of the terms which may cause some confusion. This is not a complete list of words that you may hear. There are many other common terms but we do not list them because they are uncool and shouldn't be encouraged. We do not list all of the skill abbreviations. We also do not add a link for every item.

1H - one-handed weapon
2H - two-handed weapon
A1, A2, A3, A4, A5 - Act 1, Act 2, Act 3, Act 4, Act 5
Ama - Amazon
Amu - Amulet
Ammy - Amulet
Amp - Amplify Damage
Andy - Andariel
AR - Attack Rating
Asn - Assassin
Baba - Korean for Barbarian
Barb - Barbarian
Big D - Diablo
BS - Bone Spirit
CCB - Cruel Colossus Blade
CCBQ - Cruel Colossus Blade of Quickness
CG - Short for Chipped Gems
Char - Character
Chips - Chipped Gems
CI - Cold Immune
D - Diablo
Dmg - Damage
DR - Damage Reduction
Dupe - Duplicated Item (copied illegally or due to a bug)
Durry - Duriel
ED - Enhanced Damage
FI - Fire Immune
FO - Frozen Orb
FOH - Fist of Heavens
GA - Guided Arrow
GC - Grand Charm
GF - The Grandfather or GFraizer
GG - Good Game
GIAS - Greatly Increased Attack Speed
GS - Glacial Spike
Hammerdin - Specialist Character -> Paladin
HC - Hardcore Mode
HP - Hit Points
IAS - Increased Attack Speed
IK - Immortal King Set
IM - Iron Maiden
Izzy - Izual
Java/Javazon - Amazon specializing in Javelins
Kekekeke - Korean Laugh
LC - Large Charm
Leech - someone who gains their experience by partying with higher level characters in late game areas (rather than actually playing the game)
LI - Lightning Immune
LL - Life Leech
LoD - Lord of Destruction
LvL - Level
LR - Lower Resistance
Meph - Mephisto
MD - Mana Drain
MF - Magic Find
MSLE/MSLEB - Multi-shot Lightning Enchanted Boss (RUN!)
Mule - Character used solely to store items
Necro - Necromancer
NG - New Game or Next Game
NM - Nightmare Difficulty
Paly - Paladin
PC - Price Check. This means they want to know how much something is worth
PG/PGems - Perfect Gems
PI - Physical Immune
PK - To kill another Player
PP - Party Please
PS - Perfect Skull
Pop - To drop items when PKed because you didn't fully loot your corpse
Pots - Potions
Purist - Characters who only use items they found themselves. No trading, transfering of items from other characters, or Magic Finding
PvP - Player vs. Player
PvM - Player vs. Monster
Rin - Ring
Rush - To progress rapidly through the game, usually with an escort of higher-level players, gaining experience rapidly
SC - Small Charm or Softcore
Shako - Harlequin Crest
Softcore - Alternative to Hardcore mode, normal play
SOJ - Stone of Jordan
Sorc - Sorceress
Tele - Teleport
TP - Town Portal
TS - Thunder Storm
Twink - To use a high level character to give powerful items to a low level character they couldn't have normally
Uber - Awesome, Ultimate, Elite
WF - Windforce
WW - Whirlwind
XP - Experience
Zod Slayer - Ethereal Hellslayer with Zod Rune
Zon - Amazon