Adjudicator = Either an older beta tester, or a beta tester whose skill in game or feedback out of game have been noted. They are part of the volonteers and help test the upcoming patches.
Afk = Away From Keyboard.
Afaik = As far as i know.
Aoe = area of effect.
Ap = Ability Power. The stat which boosts the effectiveness of abilities.
Ad = Atack Damage. The stat which boosts your auto atacks damage.
As = Atack Speed. The stat which boosts your auto atacks speed.
ArP = Armor Penetration.
MrP = Magic Penetration.
Atm = At the moment.
Asap = As Soon As Possible.
B = back, fall back, enemy(s) coming for you!
Back = back, fall back, enemy(s) coming for you!
Backdoor= To attack the enemies towers and base without the assistance of your creep wave.
Bp, pill, pilling = blue pilling, going back to base.
Base, basing = blue pilling, going back to base.
Buff = A temporary increase to some stat(s) or condition.
Bush = The large grass present in LoL which allows your hero to be hidden to people outside of it.
Baron, nashor, worm, roshan, red creep = The big worm boss represented by a red skull on the minimap that gives a noticeable buff to the whole team when killed.
Bait = To deliberately appear in a position to be easily ganked so as to lure 1 or more players to be counter ganked by your team or to buy some time for other activities( Backdooring, Creeping Baron, Bp'ing back to base... ).
BG= Bad Game.
Build = How a champion and its summoner is built: Skills, Runes, Masteries...
Bearon = The Ultimate League of Legend Champion.
Brb = Be right back.
Care = Be careful, enemy(s) may be coming for you!
Carry = The hero who will carry your team to victory, typically they are weak early game and require a lot of farming.
Camp, camping, camper = To wait paciently for a enemy at a certain spot.
Cba = Can't be arsed.
Cd = Ability on cooldown(not ready for use).
Creeps = The AI controlled enemies who can be found in the jungle or on the lanes.
CC = Crowd control.
Champion = The particular character that you as the summoner control in-game.
Dd = Direct damage ability.
D, def, defend = To protect against a enemy attack/push on your base.
Debuff = A temporary decrease to some stat(s) or condition.
Disable = A Disable is a debuff that prevents some kind of action on the players character.
DIAF = Die in a fire.
Dps = Damage per second. Also refers to characters whose job it is to deal the greater majority of damage in fights.
Dota = Defense of the the Ancients. A mod for War3 that launched the moba genre.
Dc, disc = disconnection from a game.
Elo = The score a person has in the Ranking system.
Emissaries = Member who goes above and beyond to help new players ease their way into the community.
Faceroll/facepalm = (easymode) rolling your face on keyboard or to be in disbelief.
Focus = To target a player. A team all focus on a specific hero to kill first.
Feed = A player who dies constantly giving xp and gold to the enemy team.
Farm, farming = To amass gold.
FFS= For F*ck Sake.
Grass = see brush.
GG = Good game.
Gd = Good.
Gj = Good job.
Gl hf = Good luck, have fun.
Gtg, g2g = Got to go.
Gank = To carry out a sudden attack on a disadvantaged enemy.
Harass = To impede and exhaust by repeated attacks or raids.
Heal = To restore health and/or to go back to base.
Hero = Non-canon name for a champion.
Inc = Incoming.
Idd = Indeed.
IP = Influence Points.
Imba = Imbalanced.
Idk = I don't Know.
Idc = I don't Care.
Jungle, jungling = The mass of trees and paths that exist between the lanes. To farm in the jungle instead of a lane.
Juke, juking, dupe = To avoid, to dodge, to fool, to escape.
Ks, Ninja = Kill steal, to deal the killing blow on a enemy hero that a ally deserved to get the gold for dealing the greater majority of damage on.
Lane = One of three roads that leads to the enemy base.
Lom = Low on mana.
Last hit = Getting the killing blow.
LoL, lol = League of Legends, laughing out loud.
Lag = To experience slower internet giving you diminishing performances.
Leave, leaver = To quit a game before it is over.
L2P = Learn to play.
Lucker = To have good luck on a random event.
Masteries = The talent-tree system of LoL.
Mb = Maybe/myBad.
Moba = Multiplayer online battle arena.
Ms = Movement speed.
Missing, miss, -1 = Used to describe when a hero is missing from a lane.
Mia = Missing in action.
Neutrals, neuts = The AI controlled enemies who can be found in the jungle.
Noob = Bad player.
Newb = New player.
N1 = Nice one.
Overfed = A player who is op thanks to to many player kills giving him xp/gold.
Oom = Out of mana.
Omg = Oh My God!
Omw = On my way.
Op= Over powered.
Pro, pgm = Professional player/gamer.
Premade = People playing a pre-selected group.
Passive = An ability which is not activatable but buffs a character.
Pb-aoe = Point blank area of affect.
Pve = Player vs Environement.
Push = To gather up your forces and destroy the enemy base.
Ping = Your internet latency.
PUG = Pick-up game.
QQ = People crying/rage quitting.
Raqequit = To quit a game in anger.
Re = Hero that was missing is now back on his lane.
Rofl = Rolling on floor laughing.
Roflmao= Rolling on the floor laughing my ass off.
Runes = Refers to LoL's rune system.
Root = A debuff which prevents any movement by a champion.
River = The river that cuts across the map diagonally.
Shop, buy = To go back to base to go shopping for items.
Sigils = Temporary buffs granted to a player by defeating the Golem and the Elder Lizard creeps.
Skillshot = An ability that fires a projectile that can be juked.
Sry = Sorry.
Stun = A debuff which prevents any action by a champion.
Silence = A debuff which prevents any abilities being used by a champion.
Support = Characters whos job is to support other characters.
SS = Miss.
Skin = Items that give Champions a new look.
Summoner = The players representation in the game.
Top, mid, bottom = The lanes in LoL.
Tele, tp = To teleport.
Tank = Hero whose job is to take damage in team fights.
Talents = A non-canon term for masteries.
Theorycraft = Making calculations of efficiency of skills/items/builds.
Tbh = To be Honest.
Ty = Thank you.
Turtling = Is to play defensive, gaining xp and gold slowly while avoiding confrontation to slowly gain a advantage over the initially stronger enemy.
Ult, ultimate, ulti = The R button ability.
Unique = A non-stackable aura/passive.
Up = Underpowered.
Vent, ventrilo, ts, teamspeak, skype, mumble = Voice communication software used to coordinate as a team.
W8 = Wait.
Wp = Well played.
WrenchMan = Part of the volonteer's to help you solve pc related problemes.
Wth = what the hell.
Yw = You're welcome.
Y = Yes.