Chat and voice communication in Counter-Strike: Global Offensive are the two most important elements of gameplay. CS:GO, just like the earlier games, is a team game, and you cannot play well without communication. Ideally, you should use a headset - if you can't, use the in-game prompts and the chat.
Throughout the years, the Counter-Strike community has created its own lexicon of different jargon terms that may seem bizarre to an outsider. Below, you can find a set of different terms and abbreviations used in CS:GO, which may come in handy. Note: there are obviously a lot more of these - we just wanted to list those most often used, and most useful for communication.
Terms and abbreviations:
ACE - All Clan Elimination - an ACE is somebody, who manages to singlehandedly eliminate all five enemies. The aces are awarded with MVP (see below).
AFK - Away From Keyboard - a standard gaming term. Use that if you need to leave the computer for a while during the game. Always inform the team if you want to leave the game and make coffee, or something. Otherwise you might get kicked.
AIMBOT - Aimhack - AIM, AH - an illegal cheat that utulizes software that helps with aiming. Most often it automatically aims at the enemies head, or automatically targets enemies. Very much forbidden.
Autonoob - it's a term for two guns in the game: SCAR-20 and G3SG1, i.e. the so-called auto-snipers (semi automatic sniper rifles). Note: using them is frowned upon during tournament games, because these weapons give a significant edge over enemies (especially among newbies). Autonoob is often used as an insult towards someone who often kills enemies with an auto-sniper.
CT - Counter-Terrorist - one of the sides of the conflict.
Clutch - a term used to describe a fight of the last of your teammates (or you) against the rest of the opposite team (more numerous). If all your teammates die, but you manage to win the round single-handedly, somebody might write "nice clutch". You can also sometimes see "clutch or kick", which means that somebody has to wind the round alone, or else they'll get kicked. It's often just a joke.
Boost - helping another player climb a tall obstacle. If somebody writes "boost me", you should stand in front of the obstacle, and press CTRL to crouch. When your teammate jumps on you, release CTRL to lift him up - they will be much higher, hence able to jump on a tall obstacle. It's often used to gain a tactical edge, such as on the map "Cache". Sometimes boost is used in different context: if an experienced player is playing with a beginner, you can say the less experienced player was boosted.
BRB - Be Right Back - another generic term, similar to AFK.
BS - Bombsite - the place where the terrorists have to plant their bomb. There are two of these: BS A and BS B. Most often you just write "A" or "B".
Cheater - or Hacker. A person using hacks or cheats, sometimes also exploits the glitches in the game, to gain advantage. In CS:GO, the most notorious examples of cheats are a wallhack (seeing through walls) and the Aimhack.
DEF - Defuse kit - a tool to defuse bombs, mandatory for a CT team.
GG, GJ, GH, GL, HF - Good Game, Good Job, Good Half, Good Luck and Have Fun - these are a matter of courtesy.
EKO, ECO - Economic - a round in which your team doesn't buy weapons to save up for next rounds. Buying a gun after an ECO was announced is frowned upon.
HS - Headshot - a shot in the head.
MVP - Most Valuable Player - a title awarded to a player that has done the best job; killed the most enemies, defused a bomb, etc. In CS:GO, MVP is symbolized by stars.
Noob - a lame player, one who doesn't learn. Offensive.
Np - No problem - used to score some modesty!
Resp - Respawn - places where you spawn after getting killed.
Rush - mostly used in conjunction with A/B. Means a coordinated, quick attack.
Smurf - highly experienced players, who have a second account on Steam and play with beginners/less experienced. Smurfs are often mistaken for cheaters, if they play very good. Smurfing is mostly frowned upon, but it's not illegal.
Wallhack - WH - an illegal cheat that allows seeing through walls. Strictly forbidden.
CS: GO weapon abbreviations:
The community of Counter-Strike mostly uses abbreviations or other terms for weapons. Below, are the most commonly used:
AK - AK-47 - the most popular terrorists' gun.
Deagle - Desert Eagle, the most powerful handgun in the game.
OP - AWP - one of the most powerful sniper rifles in the game. OP is also used to describe a weapon that's somewhat better/gives an edge over the enemy.
Scout - SSG 08 - sniper rifle.
Kevlar - bulletproof vest.
Kosa - a knife CS: GO.
Neid - grenade - frag grenade.
Smoke - smoke granade.