I have updated this since the original posting of a few years ago. While it doesn't list every single term, I hope you will find it somewhat useful.
It is NOT a replacement for reading the instructions

and if you hang around here long enough, you will pick most of this up.
Other additional links
Brief overview of bnet chat commands - There is a more detailed description
here in the Community Forum Stickies
Account closed codes IE why you just got banned
* 0 - C *
5% - generally relats to +5% all resistances small charms
7% - usually refers to a 7% magic find small charm
1337 - Leet as in 'leet speak'. Originally meant as elite. Awesome outstanding. An over used terrm now usually used to make fun of someone.
0.8/0.9/1.10/1.11/1.12 - Patches. Many changes have varied the way the game has been played. The SPF FAQ has a good explanation of version differences
10 chars - All posts need 10 characters to be able to be posted. The poster is making up the numbers
1H - one-handed weapon
2H - two-handed weapon
3/20/20 - small charm that adds 3 to maximum damage, 20 to AR and 20 to life
3d/4d Shield - A socketed shield with 3/4 perfect diamonds in it giving you 57%/76% resistance to all.
A1, A2, A3, A4, A5 - Act 1, Act 2, Act 3, Act 4, Act 5
AB (Abasin) - Amazon Basin. An online community of knowledgeable players spanning many games.
abc/ddd - abc being the game name - ddd is the password
AC - armour class
afaic - As far as I'm concerned.
afaics - As far as I can see.
afaik - As far as I know
afk - Away From keyboard
Ali Baba - Blade of Ali Baba Exceptional Unique Tulwar that gives MF and GF based on character level.
alvl - Affix Level or area level
Ama/Azn/zon - Amazon.
Amp - Amplify Damage. Necro curse to reduce enemies' resistance to physical damage. Also available as charges on some items
Amu (Ammy) - Amulet
Ancients - The Three Ancients in Act 5.
Andy - Andariel. Act 1 super unique monster.
Anni - Annihilus (the one and only unique small charm)
AoE - Area of Effect. A spell that targets an area.
AoKL - arm of king leroic tomb wand
AR - Attack Rating.
Arach - arachnid mesh belt. Unique belt that gives +1 skills
Arkaine's (Ark) - Arkaine's Valor Elite Unique Balrog Skin.
Arreat's - Arreat's Face Unique Slayer Guard.
AS - Arreat Summit. Battle.net's/Blizzard's official website for D2.
ASAP - As soon as possible.
Asn/asa/assy/sin - Assassin.
Atlantean - The Atlantean Exceptional Unique Ancient Sword.
Atm - At the Moment.
ATMA - Single player muling utility, that includes a very useful drop calculator
Atma's - Atma's Scarab Unique Amulet.
AW - The Ancients' Way in Act 5.
B.net (Bnet) - Battle Net. Blizzard's game server for Diablo II.
B/O - Best Offer. Used in trading items. Also Battle Orders a Barbarian skill
BA - Bone Armor (necromancer skill)
BA - Blessed Aim (paladin skill)
Baba (Barb) - Barbarian.
Bane - Gladiator's Bane Elite Unique Wire Fleece
Baranar's (Banana) - Baranar's Star Elite Unique Devil Star.
Bartuc's (Barts) - Bartuc's Cut-Throat Unique Greater Talons.
Basher - The Cranium Basher Elite Unique Thunder Maul
BBL - Be Back Later
BBS - Be back soon
BC (BCom) - Battle Command. A Barbarian warcry to increase skill levels.
BC (BCry) - Battle Cry. A Barbarian warcry to decrease an enemy's damage and defense
BF (BFury) - Blade Fury. An Assassin Trap Tree skill.
BF - Bloody Foothills
BG - Blood Golem
BH - Blessed Hammer (paladin skill)
Big D - Diablo
BIN - Buy it now. A fixed price, no negotiation.
BK - Bul-Kathos (unique ring/barbarian set)
Blk - Block.
bm - bad manners. Indicating a PvP ruleset
BO - Battle Orders
BoI - Blades of Ice.
boost - rush
BoS - Burst of Speed
BotD - Breath of the Dying. A v1.10 Runeword.
Bp - Breakpoint. A mark at which something improves.
BP - Bone Prison (necromancer skill)
Brb - Be right back.
Brt - Be right there.
BS (BSentinel) - Blade Sentinel. an Assassin skill on the Trap tree.
BS (BShield) - Blade Shield. an Assassin skill on the Trap tree.
BS (BSpear) - Bone Spear. A Necromancer attack skill.
BS (Bspirit) - Bone Spirit. A Necromancer attack skill.
B-Star - Barnard's star (unique mace)
Btc - Back to channel.
BTS - Blizzard Technical Support.
btw - By the way
Burrito (Buriza) - Buriza-Do Kyanon Exceptional Unique Ballista
BvB - Barbarian Versus Barbarian Dueling.
BvC - Barbarian v Caster (pvp)
BW - Bone Wall. A Necromancer skill on the Poison and Bone tree
C/C - Claw/Claw. Refers to an Assassin wielding dual claws
C/O - Current Offer. Used in trading items.
C/S - Claw/Shield. Refers to an Assassin using a claw and shield.
CA - Chilling Armor. A Sorceress skill on the Cold tree.
Cat 2 - Catacombs Level 2 in Act 1.
CB - Charged Bolt. Sorceress lightning tree attack skill.
CB - Crushing Blow.
CB - Colossus Blade. Elite Sword.
CB - Charged Bolt (sorceress skill)
CBF - Cannot be frozen.
CBS - Charged Bolt Sentry. Assassin Trap Tree skill.
CCB - Cruel Colossus Blade.
CCS - Cruel Colossus Sword
CD (CDam, CDmg) - Cold Damage
CE - Cold Enchanted.
CE - Corpse Explosion. A Necromancer attack skill on the Poison and Bone tree.
CG - Clay Golem.
Cg (grats) gz - Congratulations.
Chan? - Go to channel.
Char - Character.
chippies - chipped gems
CI - Cold Immune.
CKN (Chu) - Chu-ko-nu. Often refers specifically to the Demon Machine Exceptional Unique Chu-ko-nu Crossbow
CL - Chain Lightning. Sorceress lightning tree attack skill.
Closed - Closed Battle.net. Online play with characters saved on a Battle.net Server.
clvl - Character Level.
CM - Claw Mastery.
CM - Cold Mastery. Sorceress Cold tree skill.
CM - Community Member
CM - Council Member
CO - Current Offer
CoA - crown of Ages unique item
CoH - Chains of Honor
Conc - Concentrate/ion (paladin aura/Barbarian skill)
Conv - Conviction. A Paladin offensive aura to reduce enemy resistances.
Coop (Co-op) - Co-operative play.
CoS - Cloak of Shadows.
CoT - Claws of Thunder
CP - Crystalline Passage in Act 5.
CR (CRes) - Cold resistance.
Cranium (C basher) - The Cranium Basher Elite Unique Thunder Maul.
Crest - Harlequin Crest Elite unique Shako
Crit - Critical Strike.
CRM-Colour Rune Mod - Single Player utility that turns runes any colour
CS - Crystal sword
CS - Critical Strike.
CS - Colossus Sword.
CS - Cobra Strike
CS - Chaos Sanctuary in Act 4
CtA - call to arms (runeword)
CtC - chance to cast
CTH - Chance to Hit.
CU - Cursed
Cube - The Horadric Cube
CV - colossus voulge
cya - See you.
* D - G *
D - Diablo
D/A/E - Dodge/Avoid/Evade. Trio of Amazon defensive skills from the Passive and Magic skill tree.
D2 - Diablo II
D2C - Diablo 2 classic.
D2M - Damage to Mana
D2X - Lord of Destruction Diablo 2 expansion.
Dam - Damage
DC - Dragon Claw. A skill on the Assassin's Martial Arts Tree.
DC (D Clone) - Diablo Clone.
DD - Don't die
Decrep - Decrepify. A Necromancer curse that slows and weakens.
Def - Defense
Desynch - refers to desynchronizing with the server. That way, you appear to be somewhere other than your actual location on the opponent's screen. It is usually done by some form of very rapid movement, such as a paladin constantly charging around. Note that instant movement (such as teleport) won't do this.
DEX - Dexterity.
DF - Dragon Flight. A skill on the Assassin's Martial Arts Tree.
DL - deadline in a trade EG DL10 = 10 hours before close
dii - dii.net. A D2 reference and forum site
Dii.net - Diabloii.net. #1 Fan site of Diablo 2 and a source of vast information.
diii - dii.net. A D2 reference and forum site
Diii.net - Diabloii.net. #1 Fan site of Diablo 2 and a source of vast information.
ding - Player announcing they've just leveled
DIS - Desperately in search of
DKK - Don't Kill King (cow king)
Dmg - Damage
Doombringer (Doom) - Doombringer Elite Unique Champion Sword
DOT - Damage Over Time.
DPA - Damage Per Attack.
DPS - Damage Per Second.
DR (DR%) - Damage Reduced. Items with this mod reduce physical damage.
Dropping (of items) - The act of entering a game to present any player in that game with items as freely given gifts, to be distributed among the players in the game as they see fit.
Dru - Druid.
DS - Deadly Strike.
DS - Death Sentry. A skill on the Assassin's Traps Tree.
DT - Dragon Tail. A skill on the Assassin's Martial Arts Tree.
dupe - an item which has been duplicated. This forum doesn't condone them so don't ask
DOH - Durance of Hate
Durry - Duriel
Dvd - Damage versus Demons.
Dvm - Defense versus missiles.
Dvu - Damage versus Undead.
dweb - deaths web unearthed wand
Eagle (Eaglehorn) - Eaglehorn Elite Unique Crusader Bow.
eBotD - Ethereal breath of the dying
ED - Enhanced Defense. A mod that increases defense on an item.
ED/IAS - Enhanced Damage/IAS. Typically refers to a rare combination of mods on a jewel.
EF - Extra Fast.
eg - exempli gratia (Latin). Used to mean 'for example'.
EIAS - Effective Increased Attack Speed.
ENE (ENG. ERG) - Energy.
ES - Extra Strong.
ES (e-shield) - Energy Shield. Sorceress lightning tree defensive skill
ETF - European Trade Forum.
Eth - Ethereal.
exp - Experience
Eye (EoE) - Eye of Etlitch Unique Amulet
EZPK - easy player kill, killing another player usually by ambushing them
FA - Freezing Arrow. An attack skill on the Amazon Bow and Crossbow skill tree.
FA - Frozen Armor. A Sorceress skill on the Cold Tree.
Face - Arreat's Face Unique Slayer Guard
Fana - Fanaticism. A Paladin offensive aura to increase attack speed and physical damage
FAQ - Frequently Asked Questions.
FB - Fireball. Sorceress fire tree attack skill.
fb - Fire Bolt. Sorceress fire tree attack skill.
FB - Fire Blast. Assassin Trap tree skill.
FBR - Faster block rate
FC - Fire Claws. A Druid shape shifting skill
FCR - Faster cast rate.
FD (FDam, FDmg) - Fire damage.
FE - Fire enchanted
FG - Fire Golem
FHR - Faster Hit Recovery
FI - Fire Immune.
FI - Find Item. A Barbarian War Cry Skill.
Fishy(mancer) - Summoner necro. Nightfish wrote the guide.
Fists - Magefist Unique Light Gauntlets
Flaming - Making a personal attack or insulting remark, intended to incite anger.
Flavie - Single player reporting system that uses ATMA information and reports what sets/uniques/runes/gems the player has
FM - Fire Mastery. Sorcerees Fire Tree skill.
FN - Frost Nova. Sorceress cold tree attack skill
FO - Frozen Orb. Sorceress cold tree attack skill.
FoF - Fists of Fire. An Assassin attack skill on the martial arts tree
FoH - Fist of the Heavens. An attack skill on the Paladin Combat tree.
Forge - Hell forge quest in act IV. Hell can drop up to a Hel to Gul
Fpa - Frames per Attack
FPS - Frames per second (command needed /fps)
FR - Feral Rage. A Druid shape shifting skill.
FR (FRes) - Fire Resistance.
Frosties (Frosts) - Frostburn Unique Gauntlets.
FRW - Faster Run/Walk.
FT - For trade or Fast Trade (BIN) depending on realm
FTW - for the win
FW - Firewall. Sorceress fire tree attack skill
FWIS - For what it is worth.
FYI - For your information.
GA - Guided Arrow
Gaze - Vampiregaze Exceptional Unique Grim Helm
GC - Grand Charm
Geddon - Armageddon. A Druid Elemental Tree skill.
GF - Grandfather (sword)
gfi - Go for it
gg - good game. Standard response to your opponent after a PvP duel. Can also mean good gear. Anything good really

Gheed's - Gheed's Fortune Unique Grand Charm
Gj - Good job.
Gl - Good luck.
Gm - Golem Mastery.
GMB - grand matron bow
gosu - godly or awesome. Very good
Grail - players attempting to get one of each set/unique in the game. Usually associated with single player because of ATMA
grush - glitched rush where a level one character can get to hell. Usually to level at Uber Trist
Grandfather (gf) - The Grandfather Elite Unique Colossus Blade. D Spirit of Barbs. Gris' _______ - Piece of Griswold's Legacy set. Made for the Paladin.
GS - Glacial Spike. Sorceress cold tree attack skill.
GS - Glacial Spike. Sorceress cold tree attack skill
GSA - Goldstrike Arch Exceptional Unique Gothic Bow
gtg - Good to go (or Got to go)
Gull - Gull Unique Dagger.
GW - Grim Ward. A Barbarian War Cry Skill.
* H - K *
H - Hell. Third and last difficulty of Diablo 2.
Harley - Harlequin Crest Elite Unique Shako
HB - Holy Bolt. A Paladin combat skill.
HC - High Council (uniques found in the Travincal Act3, Durrance of hate lvl 3 Act3 and Worldstone Keep lvl 3)
HC - Hard Core. One death and game over
HCMTF - Hit Causes Monster to Flee.
Hellslayer - Hellslayer Elite Unique Decapitator
Heph - Hephasto the Armorer. Act 4 super unique monster.
HF - Holy Freeze. A Paladin offensive aura to chill enemies.
HoBL - Hand of Blessed Light Unique Divine Scepter
HoJ - Hand of Justice. A v1.10 Runeword.
Homunculus - Homunculus Unique Hierophant Trophy
Hork(ing) - Using the Barbarian skill Find Item on corpses of slain enemies can yield items, dubbed horking.
Horn (Eaglehorn) - Eaglehorn Elite Unique Crusader Bow.
Hot - Warning that a portal is dangerous to enter
HotO - Heart of the Oak. A v1.10 Runeword.
HoW - Heart of Wolverine. A Druid summoning skill
HoZ - Herald Of Zakarum Unique Gilded Shield.
HP - Hit Points.
HR - high rune - definitions vary, depending on the realm
HS - Holy Shield. A Paladin combat skill to boost shield characteristics.
HS - Holy Shock.
i.e. - That is (id est in Latin).
IAS - Increased Attack Speed/Initial Attack Speed
IB - Ice Blast. An attack skill on the Sorceress' Cold Tree.
IBS - Invisible Bone Spirit. Bone spirit no longer becomes visible if off screen. Hazard in duels. Contact your local Necro for more details.
ID - Identify.
IG - Iron Golem
IIRC - If I recall correctly
IK _______ - Piece of Immortal King's Set. Made for Barbarians.
IK Maul - Immortal King's Stone Crusher Set Ogre Maul
Ilvl - Item Level.
IM - Iron Maiden. A Necromancer Curse.
IMHO - In my humble/honest opinion.
Immo - Immolation Arrow. An attack skill on the Amazon Bow and Crossbow tree
IMO - In my opinion
Ind - Indestructible.
Inv - Inventory.
Ire - Skullder's Ire Exceptional Unique Russet Armor
IS - Iron Skin. A Barbarian mastery to increase defense
ISO - in search of
ITD - Ignore Target's Defense
Izzy - Izual. Act 4 super unique monster.
j/k - Just kidding.
Jalal's - Jalal's Mane Unique Totemic Mask
k - Okay
kk - ok
KA - Kick bum*(sensored)
KB - Knockback