A list of car parts/automotive terms beginning with the letters G through L . . . 

A means of sealing the mating surfaces between various components. Gaskets are used between the various parts of the engine to keep oil, coolant, air and fuel in their respective places. Rubber, cork or combination cork/rubber gaskets are often used to seal the oil pan, valve covers, water pump and timing chain cover. Metal gaskets are used between the cylinder head and engine block, and metal or asbestos gaskets are used to seal intake and exhaust manifolds. Over time, cork gaskets tend to become brittle and break. This allows oil to leak out of the engine (See Oil Consumption). Tightening the cover bolts will sometimes stop a leak but usually the gasket must be replaced. Some late model engines use various chemical sealers (such as RTV silicone) in place of conventional gaskets.
Wheel-shaped parts with teeth cut into the edge. When one gear engages another, the second gear drives the other to transmit power.
A unit of measure for quantifying power output. Invented by James Watt, the term was originally used to describe how much effort a horse exerted when lugging coal out of a coal mine. One horsepower was the amount of effort one horse put forth in raising 33,000 lbs (15,000 kg) one foot (30 cms)in one minute. Engine horsepower ratings are determined on special equipment called a dynanometer, and are usually expressed as so much "brake" horsepower [bhp](the amount of horsepower the engine actually delivers after internal friction and parasitic losses are taken into account).
Centre part of a wheel or gear
Hydraulic System
The delivery system of a modern braking set up. It uses fluid to transmit the force applied at the pedal to the wheel cylinders, where it can be converted back into mechanical energy to activate the brake shoes or disc callipers.
The accumulation of water in a film under the footprint causes a tyre to lift from the road surface, losing traction. Hydroplaning is affected by vehicle speed, tread pattern, and water depth.
Idle Speed
This refers to how fast the engine runs when idling. It can usually be adjusted by turning a screw on the carburetor throttle linkage, or by turning an air bypass screw on a fuel injection throttle body. On many newer cars, however, it is computer-controlled and non-adjustable.
Ignition System
The various components that control the igniting of fuel in the engine's cylinders. The ignition system has two parts: the primary side (the distributor and electronic control module), and the secondary side (the ignition coil, distributor cap, rotor, spark plug wires and spark plugs). In distributorless ignition systems, there is no distributor. Each cylinder has its own ignition coil (see Coil-On-Plug Ignition), or coils are shared between paired cylinders that are opposite one another in the firing order (See Distributorless Ignition System).
A substance added to oil, water or gas to prevent foaming or rust.
Inflation Pressure
The pressure of air inside a tyre that applies a tensile stress to the tyre cords permitting them to carry the vehicle's load. 
Input Shaft
The shaft to which torque is applied, usually carrying the driving gear or gears. 
Intake Manifold
The network of passages that direct air or air-fuel mixture from the throttle body to the intake ports in the cylinder head. The flow typically proceeds from the throttle body into a chamber called the plenum, which in turn feeds individual tubes, called runners, leading to each intake port. Engine breathing is enhanced if the intake manifold is configured to optimize the pressure pulses in the intake system.
A heat exchanger that cools the air (or, in some installations, the intake charge) that has been heated by compression in any type of supercharger. An intercooler resembles a radiator; it houses large passages for the intake flow, and uses either outside air or water directed over it to lower the temperature of the intake flow inside. The result is roughly a 10 to 15 percent improvement in horsepower.
Jumper Cables (or Jump Leads)
Cables used to conduct an electrical current from the battery of one car to another car with a dead battery, enabling the disabled car to generate its own power. With the complicated computer systems of modern cars, this is recommended only in cases of extreme emergency, and should be carried out methodically by someone who knows what they are doing.
Jump Starting
A technique of starting one vehicle using another vehicle's battery. A pair of jumper cables are required to connect the terminals of both batteries together (positive to positive, negative to negative). The safest technique is first connect the positive terminals on both batteries to one another, and then to connect the negative terminal on the good battery to a ground (such as the engine block or frame) on the vehicle with dead battery. The final jumper connection usually sparks so keeping the spark away from the discharged battery avoids any danger of blowing up the battery. Once the jumper cables have been connected, the engine should be run at fast idle to help charge the dead battery for a couple of minutes. Then the first attempt to start the car should be made. If it doesn't start within 15 seconds, stop and wait a minute before trying again. This gives the starter a chance to cool off. Continuous cranking can ruin the starter and drain the good battery.
The metric measurement equivalent to roughly five-eighths of a mile. There are 1.609344 kilometers in a mile.
1. A sound created by movement of parts in loose or worn bearings.
2. A noise caused by gasoline in the cylinders burning too quickly. Also known as detonation.
Laminated Windscreen
A windshield comprised of two sheets of glass with a thin layer of plastic in between to prevent glass from splintering upon impact. This structure also enables chipped windscreens to be safely repaired.
A viscous lubricating oil used to lubricate the steering linkage, the suspension system and other moving parts outside the engine. 
Lube Job
The greasing and lubrication of the suspension system, the drive train and other general parts of a vehicle. A total lube job should be performed professionally once or twice a year and can easily be done when a vehicle's oil is changed. 
A material such as grease or oil used to lubricate two moving parts in order to reduce friction. 
Lug Bolt
The bolts that secure the wheel to the hub.