League of Legends: Glossary

Here are some common acronyms and expressions used by the League of Legends communities and writing.

Stats:
AD - Attack Damage
AP - Ability Power
AR - Armor
AS - Attack Speed
MR - Magic Resist
MS - Movement Speed
GP5 - Gold Per 5 Seconds
HP5 - Health Per 5 Seconds
MP5 - Mana Per 5 Seconds
CDR - Cooldown Reduction
CC Reduction - Tenacity for crowd-control reduction. Makes crowd-control effects not last as long against you
DR - Damage Reduction
Crit - Critical Strike Chance

Items:
AA - Archangel's Staff
BT - Bloodthirster
BV - Banshee's Veil
DFG - Deathfire's Grasp
FoN - Force of Nature
GA - Guardian Angel
HoG - Heart of Gold
IE - Infinity Edge
LW - Last Whisper
PD - Phantom Dancer
Pot - Potion. Often Health Potion. To "pot up" sometimes means using Elixirs for additional stats.

Summoner's Rift Map:
Baron - Baron Nashor
Base - The area around the Nexus
Bot - Bottom lane
Top - Top lane
Mid - Mid lane
Dragon - The dragon spawn
Blue/Golem - The Ancient Golem's spawn
Red/Lizard - The Elder Lizard's spawn
River - The river that goes diagonally from top left to bottom right
Inhib - The inhibitors just inside the base

Combat:
Burst - When a lot of damage is dealt in a short period of time
CC - Crowd Control. Any movement or performance inhibiting ability
Disable - An ability that prohibits the unit from performing an action
DPS - Damage Per Second. Usually refers to high damage over time, rather something that spikes
Focus - To kill the specified target first
Gank - To unexpectedly go for the kill on someone, usually when outnumbered
Initiate - The one to start a fight or be the first into a fight
Kite - To move and damage an enemy while staying out of their range while they chase you
OOM - Out of Mana.
Poke - To fire abilities and attacks at ranged at the enemy then backing off to try and harassSustain - Any form of healing or regenerative effect

Abilities:
AoE - Area of Effect. Abilities that affect an area
Blink - Movement abilities where you instantly move, rather than travel toward it, like Flash
Buff - A positive persistent effect from an ability or the environment. To make stronger
CD - Cooldown
Charges - The amount of stored up subsequent casts for certain abilities, like Shadow Dance
Cone - A cone-shaped targeting ability
DD - Direct Damage. A single target damage dealing ability that deals all damage upon impact
Debuff - A negative persistent effect from an ability or the environment
Global - Has no range limit
PBAoE - Point Blank Area of Effect. Abilities affecting the area around the caster
Ratio - The ability boosts received with respect to your bonus stats. AP ratio, for example.
Skill Shot - Abilities that can be dodged and require aiming, such as Mystic Shot or Dark Binding
True Sight - The ability to see stealthed units

Tactical:
B - Back. Backing off, returning to base, or to tell someone to fall back
Bait - To lure someone unexpectedly into something, or trick them into doing something.
BD - Back Door. To attack an enemy structure without minion support away from everyone else
Dive - To go in for the kill
FoW - Fog of War. The area not currently visible to your team
Push - To advance forward, usually with the minion wave
Wave - A group of minions

Chat:
BG - Bad Game. No one likes bad games :(
Care - Be careful. May be in threat.
Carry - Performing exceptionally and winning the game for the team
CS - "Creep score". How many minions and neutrals you've killed
D - Defend. Play defensively. Defend the base or structure.
DC/Disc - Disconnect
Feed - Dying constantly with minimal to no contribution
FF - Forfeit. When people want to give up and surrender
GG - Good Game. Used to state that it was a good game. Sometimes used to indicate someone was bested, out-played, or that the game is likely over.
GL - Good Luck
HF - Have Fun
KS - Kill steal
MIA/Miss - An acronym for Missing In Action used when a champion is no longer visible, so watch out!
QQ - Crying eyes. Usually used to insult someone saying that they're whining or crying
Rage - To outwardly complain and get upset. To be angry or furious.

Miscellaneous:
Ace - Occurs when all enemy champions are killed
Penta - Pentakill. Get 5 champion kills in quick succession
Nerf - To weaken or make worse
OP - Overpowered 
UP - Underpowered