gage:

A standard SAE designation of wire sizes, expressed in AWG (American Wire Gage). The larger the gage number, the smaller the wire. Metric wire sizes are expressed in cross-sectional area, which is expressed in square millimeters. Sometimes the spelling "gauge" is also used to designate wire size. However, it is becoming standard to use "gage" for wire size and "gauge" for instruments. Americans often use "gage" for instruments.
Gallon:

A US gallon (3.785 liters) is 20% smaller than an Imperial gallon (4.546 liters).
Galvanize:

The action of plating with zinc by hot dipping or electrodeposition to protect from rust.
Garage:

[1] A building in which a motor vehicle is kept.

[2] The premises on which motor vehicles are repaired or serviced and/or where fuel is sold.

[3] To keep in a garage 

Garage jack:

A powerful hydraulic jack used in garages.
Garaged:

A reference to a vehicle which is kept in a garage, as in My car is always garaged. The abbreviation in advertisements is gar'd.

Gas:

[1] A non-solid material. It can be compressed. When heated, it will expand; and when cooled, it will contract (such as air.)

[2] A common term for gasoline. (Br) - petrol

[3] A term for LPG or propane.

[4] A term referring to the exhaust gases. See exhaust emissions.

[5] To apply the throttle.
gas gauge:

An instrument, usually located on the dashboard or center console, which indicates the amount of fuel in the fuel tank. Most gauges have a needle which fluctuates between "E" (empty) and "F" (full). Others show a digital readout of how many gallons or liters left in the tank. Also called "fuel gauge." 

gas guzzler:

A vehicle which uses a lot of gasoline per mile.
gas pedal:

The device actuated by the operator's foot for increasing or decreasing the amount of fuel entering the combustion chamber. Also called "throttle pedal."
gas pump:

A device at a service station which pulls gasoline from a storage tank (usually located underground) into the vehicle's gas tank. Commercial units also record the amount of fuel dispensed as well as the cost.
gas tank:

The container for holding or storing fuel. See fuel tank.
gasket:

A material made of asbestos, cardboard, cork, paper, rubber, or soft metal placed between two metal parts to insure proper sealing.
Gasohol:

A blend of gasoline and ethanol alcohol that usually is 90% gasoline and 10% ethanol. Ethanol is the alcohol found in intoxicating beverages. It may attack rubber and plastic parts of fuel systems not designed to handle alcohol-blended fuels, but it is not poisonous to human beings like wood alcohol or methanol.
gasoline:

a viscous fluid refined from crude oil which is made up of fossilized plant and animal remains and burned in internal combustion engines
gasoline pump:

A device which pulls fuel from an underground storage tank into a vehicle's gas tank.

gear:

Wheel-like part with teeth cut into the rim. When one gear meshes with another gear, it causes the second gear to drive the other and in this way transmits power. When the gears are different sizes (different number of teeth on each gear) the mechanical average is changed.
gear lever:

A device which is attached to the side of a steering column or to the center console which will allow the operator to change the gears of the transmission. Also called "shift lever."
gear ratio:

The relationship between the number of turns made by a driving gear to complete one full turn of the driven gear. If the driving gear turns four times to turn the driven gear once, the gear ratio would be 4 to 1. In most instances, the gear ratio is not even like 4:1 because the same teeth would be meshing with each other. Thus a ratio of 4.11:1, for instance, means that a particular tooth on one gear may eventually mesh with every one of the teeth on the other gear. Changing the tire size will change the effective gear ratio.
gearshift:

A device which allows the operator to move the transmission gears into various configurations. Most often the gearshift is located on a lever on the steering column or on a lever on the floor between the driver and front passenger. Some older Chryslers had pushbutton controls on the dash.
 GM
General Motors:

a major car company. Divisions are Chevrolet, Cadillac, Oldsmobile, Saturn, GMC, Buick, and Pontiac.
generator:

A device which allows the operator to move the transmission gears into various configurations. Most often the gearshift is located on a lever on the steering column or on a lever on the floor between the driver and front passenger. Some older Chryslers had pushbutton controls on the dash.
glove compartment:

A small compartment (often with a lock) located in the dash in front of the passenger (not the driver) into which small items (owner's manual, maps, first aid kit, etc.) are placed. glove compartment.

(Br) -  glovebox
Governor:

a device used with the carburetor to maintain constant engine speed regardless of load
gravel:

A mixture of rocks and sand where the rocks are usually less than 1 inch (25 mm) in diameter.
gravel road:

A road which is covered with a layer of gravel. Also called a secondary road or an improved road.
grease:

[1] A lubricant (made from oil and metallic soaps) which reduces the friction between moving pieces of metal and also prevents moisture from causing metal to rust.

[2] To lubricate or coat with grease.
greenhouse gases:

(GHGs) Group of gases which individually act to trap solar energy near the earth. GHGs for which emission levels have been estimated are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), sulphur hexafluoride (SF6), carbon tetrafluoride (CF4), carbon hexafluoride (C2F6) and hydrofluorocarbons (HFCs).
grille:

A grating or crosswork of bars usually as an ornamental cover of the radiator which allows air to cool the engine.
grommet:

A rubber or plastic ring around a hole in metal (to protect a cable or pipe)
gross ton:

2240 pounds. Also called "long ton."
gross weight vehicle:

(GVW) Maximum legal weight at which a vehicle can be operated. The total weight of a fully equipped truck and payload.
gut:

To strip the interior of the vehicle. May also refer to removing the internal baffles from a muffler.