0e	"Zeroth edition" [Original Dungeons and Dragons]
1e	First Edition [Advanced Dungeons and Dragons]
2e	Second Edition [Advanced Dungeons and Dragons]
3e	Third Edition [Dungeons and Dragons]
3H3L	Three Hearts and Three Lions
3LBB	Three Little Brown Books
4e	Fourth Edition [Dungeons and Dragons]
5e	Fifth Edition [Dungeons and Dragons]
AAC	Ascending Armor Class
AC	Armor Class
ACKS	Adventurer Conqueror King System
AD&D	Advanced Dungeons and Dragons
AD&D1E	Advanced Dungeons and Dragons, First Edition [1977]
AD&D2E	Advanced Dungeons and Dragons, Second Edition [1989]
AER	An Echo, Resounding
AFAIK	as far as I know
AP	actual play; armor-piercing
AS&SH	Astonishing Swordsmen and Sorcerers of Hyperborea
ASE	Anomalous Subsurface Environment
ASSH	Astonishing Swordsmen and Sorcerers of Hyperborea
B&W	black and white
B/X	Basic/Expert [Dungeons and Dragons, 1981 edition]
B1	Basic Series Module 1: In Search of the Unknown
B2	Basic Series Module 2: The Keep on the Borderlands
B3	Basic Series Module 3: Palace of the Silver Princess
B4	Basic Series Module 4: The Lost City
B5	Basic Series Module 5: Horror on the Hill
BE	Basic/Expert [Dungeons and Dragons, 1983 edition]
BECMI	Basic/Expert/Companion/Master/Immortal [Dungeons and Dragons, 1983 edition]
BFRPG	Basic Fantasy Role-Playing Game
BRP	Basic Role-Playing
BTB	by the book
BTFO	blown the fuck out
BtW	Beyond the Wall
BTW	by the way
BX	Basic/Expert [Dungeons and Dragons, 1983 edition]
C&C	Castles & Crusades
CHA	Charisma
CR	challenge rating; Critical Role
CoC	Call of Cthulhu
CON	Constitution
CSIO	City-State of the Invincible Overlord
D&D	Dungeons and Dragons [any version]
DC	Difficulty Class
DCC	Dungeon Crawl Classics
DCO	Deep Carbon Observatory
DEX	Dexterity
DIY	do-it-yourself
DM	Dungeon Master
DMG	Dungeon Masters Guide
DnD	Dungeons and Dragons [any version]
DR	Damage Reduction
DTRPG	Drive-Thru RPG
EE	Esoteric Enterprises
EXP	experience points
FAQ	frequently asked questions
FF	Fiend Folio
FLGS	friendly local game store
FOE	False OSR Enthusiast
FOEGYG	False OSR Enthusiast, Get Ye Gone
FR	Forgotten Realms
FTD	Five Torches Deep
GIMP	GNU Image Manipulation Program
GLOG	Goblin Laws of Gaming
GM	Game Master
GP	gold pieces
GURPS	Generic Universal Role-Playing System
GW	Gamma World; Games Workshop
GYG	get ye gone
HD	hit dice
HEMA	Historical European Martial Arts
HP	hit points
I6	Intermediate Series Module 6: Ravenloft
IDK	I don't know
IIRC	if I remember correctly
IMHO	in my humble/honest opinion
IMO	in my opinion
INT	Intelligence
IRL	in real life
ItO	Into the Odd
ITT	in this thread
JG	Judges Guild
JRPG	Japanese [video] Role-Playing Game
KLOWN	Kindly Little Old Warrior Noble
KS	Kickstarter
L5R	Legend of the Five Rings
LBB	Little Brown Books
LL	Labyrinth Lord
LOL	laughing out loud
LotFP	Lamentations of the Flame Princess
LotR	Lord of the Rings
LVL	level
M/U	magic-user
MCC	Mutant Crawl Classics
MM	Monster Manual
MM2	Monster Manual Two
MMO	massively-multiplayer online [role-playing game]
MtG	Magic: the Gathering
MTG	Magic: the Gathering
MTM	man-to-man
MU	magic-user
NAYRT	not [the] anon you're responding to
NPC	non-player character
NTYART	not the anon you're responding to
NuD&D	"Nu"-Dungeons and Dragons [late 2nd-5th+ edition]
OA	Oriental Adventures
OC	original character
OD&D	Original Dungeons and Dragons [1974]
OGL	Open Gaming License
OOC	out-of-character
OP	original poster; over-powered
OSE	Old-School Essentials
OSR	Old-School Roleplaying/Renaissance
OSRG	Old-School Roleplaying General
OSRIC	Old-School Reference and Index Companion
PbtA	Powered by the Apocalypse
PC	Player Character
PDF	Portable Document Format
PF	Pathfinder
PHB	Players Handbook
PLOG	Possum Laws of Gaming
POD	print on demand
PoV	point of view
PTSD	Post-Traumatic Stress Disorder
PvP	player versus player
PWYW	pay what you want
RAW	rules-as-written
RC	Rules Cyclopedia
RIP	rest in peace / requiescat in pace
RPG	role-playing game
RQ	Runequest
S&S	swords and sorcery
S&W	Swords and Wizardry
SJW	social justice warrior
SP	silver pieces; Scrap Princess
SRD	System Reference Document
STR	Strength
SWN	Stars Without Number
T&T	Tunnels and Trolls
T1	Temple Series Module 1: The Village of Hommlet
TFT	The Fantasy Trip
THAC0	to-hit Armor Class Zero
TL;DR	too long, didn't read
TotSK	Tomb of the Serpent Kings
TPK	total party kill
TSR	Tactical Studies Rules
TTRPG	table-top role-playing game
UA	Unearthed Arcana
UVG	Ultraviolet Grasslands
VotE	Veins of the Earth
VtM	Vampire: the Masquerade
VTT	Virtual Tabletop
WEG	West End Games
WFRP	Warhammer Fantasy Roleplay
WIP	work in progress
WIS	Wisdom
WoD	World of Darkness
WotC	Wizards of the Coast
WoW	World of Warcraft
WP&WS	Wolfpacks and Winter Snow
WTF	what the fuck
X1	Expert Series Module 1: The Isle of Dread
XP	experience points
YMMV	your mileage may vary
~ZOZ	[undefinable]