I noticed there isn't a list of abbreviations commonly used in the chat. At least I couldn't find one!
New players might have trouble making sense of the plethora of terms used in chat by experienced players, and I've seen newbies asking what "SBH" means" quite often. So, here is an attempt to list those abbreviations along with their meaning. If you have any additions, please put them in a comment and I will add them if appropriate. Mods may feel free to make this a sticky if they want.
Arty - Nod's artillery.
Arty Party - A large (usually 4+) number of artillery pieces used to attack the GDI base. A favourite Nod tactic on maps like Whiteout and Islands. Dangerous when unchecked because of the extremely high damage output from a long distance.
Bar - GDI Barracks
Chem - Nod Chem Trooper. Basically beefed-up Flamethrower infantry. Primarily used in early-game rushes.
Chin - Chinook transport helicopter. Basically a flying APC. Destroy incoming enemy Chinooks as soon as possible.
Chopper - Helicopters of all sorts (Orcas, Apaches, Chinooks)
Inf path - The map's infantry path leading to the base, which is inaccessible to vehicles. An example are the tunnels connecting the bases on Field.
Doza - Mendoza, a high-tier Nod infantry killer.
Engie - Low tier Engineer.
Field Tech / Field Hottie - Engineers that are not used as part of the base defense, but rather support the vehicles (and combat infantry) in the field by repairing and healing them. Since they are only armed with pistols and C4, they have to be protected from all threats, especially stealthed units and snipers.
Ion/Nuke - The superweapons of GDI and Nod, respectively. When planted, their beacons emit a beeping sound and a faint glow.
Flamer/FTank - Nod Flame Tank
Harv / Harvy - Tiberium harvester
HON - Hand of Nod
Hottie - Hotwire. GDI's advanced engineer class.
Inc - Incoming! When you see this in chat, prepare to defend the base from an oncoming attack.
LCG - Nod Laser Chaingunner
LTank - Nod Light Tank
MCT - Master Control Terminal. Each building has this. It serves two functions: When repaired, the building it is in is repaired quicker, and when attacked (by C4 or shooting), it deals more damage to the building.
Field - A general word for the no-man's land between both bases, where the majority of fighting commonly happens. Also the name of a map.
Med - GDI Medium Tank
MINES - When you see this in chat, immediately check the base for missing Proximity C4s and infiltrators, and remine as soon as possible.
Mob - Moebius, a high-tier GDI infantry class, armed with a very powerful but short-range lightning gun. Dangerous to vehicles and infantry alike.
PP - Power Plant
Ref - Tiberium Refinery
Rush - A coordinated assault, often consisting of one class or type of vehicles or infantry (for example, a Med Rush would be a nothing but Medium Tanks).
SBH - Stealth Black Hand. Nod's stealthed infantry, only visible from up close as a blue shimmer. Detection range is even smaller when in a vehicle.
Stank - Nod Stealth Tank
Strip - Nod Airstrip
Tech/Techie - Nod Technician, equivalent to GDI's Hotwire.
Tib - Tiberium field, referring to the area the tiberium harvesters go to harvest
WF - GDI Weapons Factory