This glossary was compiled by Don B at jaguarforums.com and is reproduced here
with his permission

g/sec = Grams-per-second, unit of airflow measured by the MAFS
Gaiter = Boot, a covering of rubber, plastic, or leather that protects against dust & other contamination
gal or GAL = Gallon(s)
Gallon, Imperial or British Imperial = 4.546 Liters = 1.2 U.S. Liquid Gallon
Gallon, U.S. Liquid Gallon = 3.79 Litres = 0.8337 Imperial Gallon
Gas = Gasoline, Petrol; any gaseous substance
Gasket = Rubber, plastic, metal, leather or cloth seal for mating surfaces between two or more parts
Gasoline = Fuel, Petrol
Garage = Shop, Repair Shop
Gaydon = Jaguar Land Rover Gaydon Centre, principal engineering headquarters
GDO = Garage Door Opener
Gearbox = Transmission, Trans, Trannie, Box
Gedore = Germany-based OEM of adjustable wrenches in Jaguar tool kits
Gel Cell = Type of VRLA battery in which silica dust is added to the electrolyte to form a paste
GEM = Generic Electronic Module, Bosch ECU for ZF Servotronic electronic steering racks
Generator = Alternator (AC) or Dynamo (DC)
Girling, Albert H. = Inventor of SS & Jaguar drum and disc brake systems manufactured by Lucas
Giubo = Flex Disc, Flexible Coupling, Jurid, named for inventor Giunti Boschi, often misspelled Guibo
Global Opening/Closing = Opening/closing all doors, windows, sunroof/moonroof with key or remote
Glove Box = Glove Compartment or Cubby Box
Glove Compartment = Glove Box or Cubby Box
GND = Ground, Earth
GOR = Grille Opening Reinforcement
GPC = Glow Plug Control
GPC = Glow Plug Control Module
GPL = Glow Plug Lampe
GPS = Global Positioning System (Sat Nav) (see NAV, NCM)
Grommet = Ring or eyelet, often a rubber ring that protects wires passing through a hole in a metal part
Ground Bus = Earth Bus, circuit to which multiple components are grounded/Earthed
Ground = Earth (see Common)
Grub screw = Allen screw, Set screw
GSM = Group Spécial Mobile/Global System for Mobile Communications mobile telephony standard
GT = Grand Touring car, a 2-door in the coupe/convertible style designed for comfort and high speed
GTR = Global Technical Resource, Jaguar onine resource for dealers and technicians, now TOPix
Gudgeon Pin = Wrist Pin, piston-to-connecting rod pin
Guibo = Misspelling of Giubo
GVW = Gross Vehicle Weight
GWM = Gateway Module
GYRO = Gyroscope, Gyroscopic Sensor