Below is the MMORPG terms glossary, using in Final Fantasy XI and Final Fantasy XIV.

Terms Meaning
Add Additional enemies, enemies that join the battle after it started.
AF Artifact equipment, also called AF1.
AF2 In Final Fantasy XI, the Relic Armor sets were often referred to as AF2, but usage of the term has gone down since the Empyrean Armor set was released. In Final Fantasy XIV it is a set of level 90 equipment that can be bought with Allagan Tomestone of Mythology. They're not the real Artifact Equipment 2, but players still calling them AF2 anyway. Also known as Myth gears and i90 gears.
AFK Away from keyboard.
Aggro A mob that noticed and attacking a player.
Alt Alternate character.
AoE Area of Effect, used to refer to spells or abilities that affect multi targets.
Bio A player who is away from keyboard for a comfort break.
BRB Be right back.
Bot Illegal form of gameplay where actions of a character can be automated to perform.
Buff Boosting of character attributes and/or abilities.
Camping Staying at specific spot to do something.
Cap/Capped The upper finite limit for any stat effectiveness or accumulated item.
Chain Pulling The act of pulling several groups of enemies in a dungeon so that they can all be brought down at the same time with area of effect abilities, in order to speed up the dungeon. Typically only done when the party's level or equipment outstrips the content in the dungeon. Many dungeons in Final Fantasy XIV employ gates that only open when certain enemies are killed in order to prevent excessive chain pulling.
Coil Refers to the Binding Coil of Bahamut in Final Fantasy XIV. In later versions, the player call it "BCoB"*(Binding Coil of Bahamut), "SCoB" for the Second Coil of Bahamut, and "FCoB" for the Final Coil of Bahamut.
Crowd Control To stop a group of enemies by stunning or sleeping.
Daily/Dailies Refers to any quest or content that may be repeated once per day, e.g. Beast Tribe quests in Final Fantasy XIV.
DD Damage dealer, an attacker role such as Black Mage, Dragoon, Monk, etc.
DF Duty Finder
Debuff Decreasing of character attributes and/or statuses.
DoT Damage over time, abilities or spells that deals damage over a period of time.
DL Darklight gears, sets of level 70 equipment in Final Fantasy XIV. Could be bought with Allagan Tomestones of Philosophy; later moved to newer dungeons.
DPS Damage per second, used to refer to the amount of damage that a character or a party can do to the enemies in specific period of time. Also used in Final Fantasy XIV to denote the role of damage dealing classes.
DPS Check A phase in battle in which the party must inflict a set amount of damage within a set period of time. Failing a DPS check often results in a wipe.
Elitist High profile players that have a classist attitude towards lower rank players.
Endgame Refers to content only accessible upon completing the storyline portion of the game.
Enrage A state that a boss may enter, which usually allows them to wipe a party with a single attack (known as a hard enrage) or becomes progressively stronger until it deals more damage than the party can heal or mitigate through (known as a soft enrage). Many bosses enrage after a certain amount of time has passed or after a party has failed a mechanic.
Farming Doing something over and over to obtain specific items.
FC Free Companies, that players may join or create.
GIRL Guy in real life, a player who's playing a female character, but is a guy in real life.
GCD Global Cooldown, abilities that share the same recast timer and can only be activated once per player turn are said to lie on the global cooldown.
GC Gears Grand Company Gears, equipment that can be purchased with Company Seals.
GG/GJ Good Game/Good Job, often used as congratulatory response completing an objective (or as a sarcastic response to a wipe).
GM Game Masters, Square Enix staff members.
Grief/Griefing An act of a player who keeps doing bad performance on purpose in order to make other players fail to do something.
Grind/Grinding To do something over and over in order to earn EXP, or some other objective.
GS Gold Saucer, an area in Final Fantasy XIV.
Hate Another word for Enmity.
Healer A role of players who's healing other players, White Mage for the example.
HoT Healing over Time. Abilities or effects that restore HP over time.
Hunt Refers to Elite Marks from the Hunt system in Final Fantasy XIV, open-world Notorious Monsters that can be defeated for Allied Seals and Allagan Tomestones.
Inv/Invite A request, typically in /shout, in Final Fantasy XIV to be quickly invited into a party for Elite Marks (or in some cases FATEs).
IRL In real life.
Kick/Kicking The act of dismissing a party member from the party.
Kite/Kiting To lure an enemy or a group of enemies around while allowing other players to attack them.
Kill Stealing Attacking an enemy that is already in combat with other players.
L2P Learn To Play, a derogatory term used to criticize other players of lower skill.
Leecher A lazy player who doesn't really help the party to fight in dungeons. The worse type of leecher will just stay at the dungeon entrance, waiting for everyone to clear the dungeon and earn rewards for him.
LFG/LFP Looking for group/Looking for party, used when a player ask to join a party.
LFM Looking for members, used when a party leader looking for party members.
Merc Mercenary, a group of top players who's carrying other players through dungeons or boss fights for amounts of gil.
Mob A monster, An enemy.
Mod Modification of the game clients. Some mods are illegal but some are allowed by Square Enix.
MT Mistell, used when a player sent a message in the wrong chatbox.
MT/Main Tank The tank who's tanking the main boss.
Mule An alternate character that use for extra inventory.
Nerf/Nerfing To reduce the power of a class/job, ability, item, etc. in order to make the game more balance. May also refer to the development team artificially reducing the difficulty of content.
Newbie New player.
Ninja A secret game update that Square Enix didn't tell the players.
NM Notorious Monsters, boss enemies that randomly appears on the open world map.
No bonus Parties who require all party members to have previously cleared the content. This term originates from the bonus in experience points or currency announced at the start of the duty which all party members receive if the party contains at least one player who has not previously cleared the content.
Noob An insulting form of Newbie.
NP No problem.
NPC Non-player character.
Nuke Spells that deals high "burst" damage.
OGCD Off Global Cooldown. Abilities that have a separate (often longer) recast time to abilities that lie on the global cooldown.
OOM Out of MP.
OT/Off-Tank The tank who's not tanking the main boss. Usually tank boss slaves.
Pet A pet that help the players in combat, such as Companion, Avatar, and Egi.
PF Party Finder.
Pony Horse-type mount, including Unicorn, Slepnir, Kirin, and most of the mounts that look like a horse. However, most players use this term to refer to horses that can be obtained from Extreme Primal trials.
PuG Pick up group, Forming party with strangers. PUG also means Pugilist in Final Fantasy XIV.
Pull/Pulling To start a combat with an enemy, usually tankers will be the one who start pulling.
QQ An insult towards a player who complains about the game features.
Queue To sign up for the Duty Finder.
Raid A high-level duty (typically a dungeon) that is typically high in difficulty and usually requires a larger sized party to complete. Raid may also refer to the party that undertakes such duties.
Rage Quit The act of abandoning an instance in response to a wipe.
Relic Relic Weapons, the ultimate weapons for each job.
Reset Moving an enemy in Final Fantasy XIV beyond a certain range, causing it to lose aggro and return to its starting point with full health.
Rez Resurrection, Raise (Life 1).
RMT Real money trader, Gil seller, people who's selling in-game Gil for real money (illegally).
Soldiery A term used for the Gerolt Masterworks equipment in Final Fantasy XIV, which are purchased with Allagan Tomestones of Soldiery.
Speedrun To clear a dungeon as fast as possible in order to make Allagan Tomestones in Final Fantasy XIV.
Stack/Stacking A directive to cluster together, such as in anticipation of an attack. Can also refer to cumulative buffs/debuffs.
Sprout A new player in Final Fantasy XIV visibly identified by a sprout icon next to their name. The sprout icon disappears upon either 168 hours of play or completion of the main scenario up until patch 2.55.
Static A party comprised of the same players who play alongside each other across an extended period of time to complete difficult content.
Tank/Tanker A role of player who's taking damage from enemies while allowing party members to attack.
Tank-killer/Tankbuster An attack or combination of attacks employed by an enemy (usually a boss) that deals an abnormally high amount of damage against a party member (usually a tank) which places the player at a high risk of being killed by it.
Tomes Allagan Tomestones, the special currency in Final Fantasy XIV.
Train/Training Pulling a large group of enemies and kill all of them together in order to earn EXP or pulling enemies to kill other players on purpose.
Trash A collective term for mobs that exist before a boss or between bosses in dungeons.
Turn #/T# Refers to individual segments of the Binding Coil of Bahamut. Turn 6-9 is often used as shorthand for Turn 1-4 of the Second Coil of Bahamut, and Turn 10-13 is often used as shorthand for Turn 1-4 of the Final Coil of Bahamut.
Wipe/Wiped The death of the entire group of players.
WTB Want to buy.
WTS Want to sell.
Zerg A strategy where a large group of players attack on enemies. It requires little to no skill, FATE in Final Fantasy XIV is a good example.