This is not meant to be a comprehensive list of acronyms related to role-playing games. Instead, it's a list of acronyms you're likely to see in my own blog. Hopefully I'll be able to embed a link to this list in the design template of my blog so people can easily reference it from any post.
List of Acronyms
1e, 2e, 3e, 3.5e, 4e - Editions of Dungeons & Dragons. I think I've also seen "0e" (see OD&D) used before in reference to the original game, back before the hard-backed books, back when the rules appeared as three separate soft cover magazines. I first picked up the game after that, in late 1979, back when it was just called "Advanced Dungeons & Dragons," which we now refer to as "1e."
3.75 - Pathfinder RPG is sometimes called this, since it was based on D&D 3.5e and features some changes.
AC - Armor Class.
AD&D - Advanced Dungeons & Dragons. They got rid of "Advanced" with 3rd edition. There used to be a "Basic" edition (called just "Dungeons & Dragons") that was simpler by comparison.
BBEG - Big, Bad, Evil Guy. Usually the head honcho opponent that characters face at the end of a given adventure.
CE - Chaotic evil, an alignment.
CG - Chaotic good, an alignment.
CHA - Charisma, an ability score in D&D and related games.
CMB - Combat maneuver bonus, a Pathfinder-specific stat for non-standard combat actions such as grappling.
CMD - Combat maneuver defense, a Pathfinder-specific stat for resisting non-standard combat actions such as grappling.
CN - Chaotic neutral, an alignment.
CON - Constitution, an ability score.
CR - Challenge rating, for determining the relative difficulty of an encounter.
CRPG - Computer role-playing game.
D&D - Dungeons & Dragons.
dn (as in d4, d6, d8, d10, d12, d20) - A shorthand notation for referencing dice. The number (n) following the 'd' refers to the type of dice, or number of sides of the dice. A number before the 'd' indicates the number of times to roll that type of die. For example, "3d6" means roll three six-sided dice and add the results to determine the total.
d% - Shorthand notation for percentile dice, i.e., two d10, but instead of adding the results, one result represents the tens column and the other becomes the ones column. In this way two d10's can be used to get a result between 1 and 100. A roll of 3 and a roll of 7, for example, would yield a result of 37.
D20 - A rules system upon which many role-playing games are based, where a 20-sided die is the one most commonly used. Introduced by Wizards of the Coast for D&D 3e.
DC - Difficulty class, a number you have to meet or exceed with a roll of a 20-sided die (plus your bonuses) in order to succeed in some attempted action.
DEX - Dexterity, an ability score in D&D and related games.
DM - Dungeon Master, D&D's equivalent to the more generic terms Game Master or referee.
GM - Game master, the "referee" for an RPG.
GP - Gold pieces.
Homebrew - Custom made by the GM, as opposed to purchased. This can apply to dungeons, adventures, or whole world settings.
HP - Hit points, the number of points of damage you can take before dying or falling unconscious.
INT - Intelligence, an ability score in D&D and related games.
LARP - Live action role-playing. Think playing games in costume.
LE - Lawful evil, an alignment.
LG - Lawful good, an alignment.
LN - Lawful neutral, an alignment.
Mini - Miniature figurine used to represent a character, NPC, or monster on a play mat.
MM - Monster Manual, a D&D-specific book.
MMO - Massively Multi-player Online, as in, "World of Warcraft is a MMORPG."
N - Neutral, an alignment.
NE - Neutral evil, an alignment.
NG - Neutral good, an alignment.
NPC - Non-player character, or characters/creatures role-played by the game master as opposed to the players (see PC).
OD&D - "Original" Dungeons & Dragons, published in 1974, before the hardcover AD&D books. The "original" has been added posthumously.
ORPG - Online Role Playing Game, or computer RPG you can play online.
PC - Player character, the character role-played by a player.
PF - Pathfinder, published by Paizo, which is both a set of published adventures (in their setting, Golarion), and a game system (see PFRPG) with which to play them.
PFRPG - Pathfinder Role-playing Game. Similar to D&D 3.5.
RPG - Role-playing game. In this blog, unless I state otherwise, when I say RPG, I mean TTRPG (see below).
STR - Strength, an ability score in D&D and related games.
SW - Savage Worlds, an RPG.
THAC0 - To Hit Armor Class Zero (but often pronounced "THAK - oh"), a stat that was used back in 2nd edition AD&D.
TPK - Total Party Kill, when every character in the party dies.
TTRPG - Tabletop role-playing game, like Dungeons & Dragons, Pathfinder, Savage Worlds, Faery's Tale, Star Wars, Marvel Super Heroes, etc. (sorry if I didn't list your favorite!)
WIS - Wisdom, an ability score in D&D and related games
WOTC - Wizards of the Coast, producers of Dungeons & Dragons and the trading card game, Magic: The Gathering. Owned by Hasbro.
XP - Experience points, awarded to characters for their accomplishments, and applied toward character advancement (e.g., at 2000 xp you reach 2nd level).