This is NOT meant to be the definitive terms list. It's here mostly to help out beginners on the Type III email list.
AFAIK = As Far As I Know
Aerial = antenna
AT = Automatic Transmission
ATDC = After Top Dead Center
BDC = Bottom Dead Center
big-end bearing = rod bearing
bonnet (engine cover) = hood
boot (luggage cover) = trunk
BTDC = Before Top Dead Center
bulkhead = firewall
bush = bushing
cabrio = convertible
crown wheel = ring gear
Darkside = custom vehicle, deviating from stock.  Taken from Star Wars.  Darksider is someone who doesn't think every car should be restored to original (stock) condition.
dizzy = distributor
Doppelgelenkhinterachse = German for IRS or Independant Rear Suspension (double joint rear axle in German)
dub = short for "vee dub" [Volkswagen or VW (vee-double-yew)]
dynamo = generator(DC)
estate car = station wagon
Fasty = Fastback
FB = Fastback
FI = Fuel Injection
FLAPS = Friendly Local Auto Parts Store
FWIW = For What It's Worth
gudgeon pin/small end = wrist pin
IMO = In My Opinion
IMHO = In My Humble Opinion
inner wing = wheel well
ISTR = I Seem To Recall
Lightside = stock vehicle.  Lightsider is a person who believes a car should remain stock (be restored).
methylated spirit = denatured alcohol
MT = Manual Transmission
NB = I've only heard this in reference to "New Beetle".  On the list we generally call a Notchback simply it's name or just "Notch"
Notch = Notchback
paraffin = kerosene.  Be careful about this one since "paraffin" can mean wax in American
Pendelachse = German for swing axle
pinking = pinging
PO = Previous Owner
POS = Piece Of Shit
propeller shaft = drive-shaft
quarter-light/wind wing = vent-wing
quarterlight = quarter/vent window
razorback = Type 34 (the 'sporty' version of the Type 3...neat cars!)
rocker cover = valve cover
saloon = sedan
SB = Super Beetle.  Long-time acronym.  Don't confuse it with "Squareback"
Schraeglenker = German for semi-trailing arm
spanner = wrench
speedo = speedometer
Square = Squareback
swarf = metal chips or debris
tach = tachometer
TDC = Top Dead Center
Variant = another name for the Type 3
vert = convertible
wing = fender
wing beading = fender welt
YMMV = Your Mileage May Vary (your results may be different)

If you plan on using a long word or group of words several times in a message but don't want to write it out every time, then properly 'set up' the acronym before using it. You can go ahead and use the acronym immediately, just make sure you follow the first instance with the full word enclosed in parenthesis.

---For Example---
It has been my opinion that the SB (Squareback) was one of the best vehicles to come from the Porsche drawing boards. The SB employs a flat, or "pancake", engine. Many who have driven a SB find it to be simply the best family wagon around.
---End Example---