A unit: A diesel locomotive with a cab for the crew.

Adhesion: The frictional grip of the wheels on the rails.

Availability: The amount of time, usually expressed as a %, that a locomotive is available for service and not down for repairs.

B unit: A diesel that does not have a cab for a crew. It is designed to be used with an A unit. Multiple Unit(MU) connections allow the A unit to control it.

Cab: A compartment in the diesel where the crew operates the locomotive.

Cab unit: A diesel with a full-width body in which the carbody is vital to the structural integrity of the unit. A cab unit has no exterior walkways.

Covered Wagon: A common nickname for a cab unit.

Cylinder: The chamber in which the piston is contained.

Diesel: An internal-combustion engine in which the fuel is ignited in the cylinders by compressed air and requires no spark plugs.

Diesel-electric: Essentially an electric locomotive that is powered by a diesel engine that is connected to a generator or alternator. The electricity generated runs traction motors that, in turn, powers the axles.

Dynamic Braking: A process in which the traction motors of a diesel are turned into generators powered by the train's wheels. This creates a great deal of heat that absorbs the motion of the train and gently slows it down. The extra heat is dissipated into the air by a bank of resistor grids on the top of the locomotive. Dynamic braking greatly reduces the wear-and-tear on the braking systems of a locomotive.

Fuel Injection: A device that sprays a precise amount of fuel, through a fine nozzle, into the cylinders.

Hood unit: A diesel locomotive in which the carbody is simply a shell that covers the frame and does not play a role in the structural support of the locomotive, as in a cab unit. The carbody is usually not as wide as the frame and this allows external walkways to be provided. The engine compartment can also be accessed from the outside of the unit.

Horsepower: The rate of doing work. Each unit of power is equal to 33,000 foot-pounds, per minute.

M.U. (Multiple Unit): The ability to connect a number of locomotives and control them from the cab of one unit. This reduces labor costs.

Piston: A disk-shaped object that fits in a cylinder and moves under pressure from fluid or gas.

Prime Mover: The diesel engine of a locomotive that powers a generator or alternator that, in turn, powers the traction motors.

Road Switcher: A hood unit suitable for both switching and freight duties.

Traction Motors: Electrical motors that, after receiving electricity from a generator or alternator, power the axles of a locomotive.

Tractive Effort: A system of measurement of the force exerted by the prime mover on the driving wheels of a locomotive. This is the standard way of measuring the power of a locomotive.

Trucks: The wheel assemblies of locomotives.

Turbocharging: The exhaust from the diesel is used to increase the pressure in the cylinders of the locomotive. This results in a large increase in power from the engine, sometimes as much as 85%! (Usually much lower)

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