It would take a book to list all the terms used to describe trains, and some are rarely used anyway.   So, for simplicity, I'm including only more common terms.

EMD: Previously Electro-Motive Division of General Motors; now owned by Greenbriar and known as Electro-Motive Diesel.  Once the undisputed king of locomotive manufacturing in North America, EMD now receives tough competition from General Electric.  Most locomotives purchased by Canadian railroads (and all built within the last few years) were built at EMD's Canadian subsidary General Motors Diesel's plant in London Ontario, though differences between locomotives of the two were very minor. 

EMD road diesels can be told by smooth, geometric hoods with two to four fans at the back (or at either end on early Geeps) and rectangular radiator intakes at the top on the sides.  Fuel tanks are almost always gracefully rounded but cabs are sharp and angular.  The most recent units are losing their smooth looks in favour of angles and boxes that coincide with the increasing internal complexity.  Click here for drawings.

GE: General Electric.  Though late in starting to build their own locomotives, GE has steadily improved their offerings, especially over the past two decades, so that they edged past EMD in sales in 1983 and have held the lead since.  GE locomotives are built at the company's Erie, Pennsylvania plant.

Early GE diesels had a distinctive snub-nosed appearance and rounded edges while later ones began the radiator wings that are one of the primary identifying features of modern GE diesels.  Angled fuel tanks, bumps and boxes all over but an overall proportional appearance characterize recent GEs.  Click here for drawings.

ALCO/MLW/BBD:American Locomotive Company. Once a great builder of steam locomotives, ALCO switched to diesel in the 1940s after the spectacular successes of EMD's early units.  Though the company quit the business in 1969, many of ALCO locomotives are still in operation today on smaller railroads.  ALCO locomotives were victims of being in a minority compared to EMD units and, as such, their increased (or possibly just "different") maintenance requirements didn't find favour with many roads.  They were, however, well-known for their good pulling ability.

ALCO units are often railfan favourites for their burbling engine sounds, well-proportioned styling and billowing smoke when accelerating.  Click here for drawings.

Montreal Locomotive Works (MLW) became the Canadian ALCO affiliate in the diesel era, and produced diesels very similar to those of ALCO prior to 1969, when ALCO left the business.  After that point, MLW further refined ALCO designs, and locomotives eventually evolved that were unique to MLW.  MLW was purchased by Bombardier (BBD) in 1982.  BBD left the domestic locomotive business in 1985, but MLW and BBD units can still be seen across the country in small numbers. Click here for drawings.

MK/MPI: Morrison-Knudsen, later MotivePower Industries, is a well-known rebuilder that only recently entered the locomotive building business.  Their units range from the MP1500D and MP2000D diesel switchers (aka EMD GP15D and GP20D) to the natural-gas powered MK1200G and the high-horsepower MK5000C.  Commuter engines in particular are often MK/MPI rebuilds.  While they share certain aesthetic features with EMD, they generally are eye-catchers for spotters. Click here for drawings.

BLW: Baldwin Locomotive Works.  Baldwin was a well-known builder of steam locomotives and dabbled briefly in the diesel market.  They produced several famous locomotive models including the DR-12-8-30 "Centipede" and "Sharknose" cab units, but never produced locomotives in numbers as large as EMD.  Baldwin left the locomotive market in 1956.  Click here for drawings.

FM/CLC: Fairbanks-Morse, and Canadian subsidary Canadian Locomotive Company.  This was a diesel-only builder that produced first-generation locomotives designed to supplant steam power.  They included the H-liner hood units and C-liner cab units, well-known for husky and pleasing carbody lines.  But F-M's distinguishing characteristic was the opposed-piston engine, in which two pistons worked outward from a combustion chamber in the center of the cylinder.  These engines were capable of generating roughly twice the horsepower from a given number of cylinders compared to conventional V-engines, but the complexity of having two crankshafts (among other things) was a cause of maintenance headaches.  F-M left the locomotive business in 1963.  Click here for drawings.

See Rolling stock Manufacturers section

AC: Alternating current.  Though locomotives have been producing it for decades and reverting it back to DC for the motors, it's only been in the last nine years that AC has caught on as a type of electricity for the locomotive traction motors.  This leads to greater traction and power (and price) as well as lower maintenance.

Alternator: A lower-maintenance version of a locomotive generator that produces AC instead of DC current.  The lack of carbon brushes is the reason for greater reliability.  The AC electricity generated is rectified back to DC before going to traction motors, even on AC-powered locomotives.

Bearing: Connection between the rotating axle and the truck frame.  Roller bearings have been used in most locomotives manufactured after 1940 and train cars after 1960.  Also describes the connection around any other axles, such as in motors.

Continuous Tractive Effort (CTE): Locomotive pulling power.  Continuous tractive effort is how much a locomotive can pull when going at the minimum sustainable speed before the traction motors overheat.  At low speeds such as this, CTE is related to locomotive weight and adhesion--generally, it's the greatest pulling power possible before the wheels begin to slip.

At higher speeds, CTE is affected by locomotive horsepower--a locomotive with more horsepower will maintain more pulling power at speed; at this point, traction is no longer an issue.  That's why a 4-axle unit and a 6-axle unit of the same horsepower will be able to pull the same train if the speed is above 20 mph or so.

DC: Direct current.  This has been the standard since 1939 for powering locomotives, and DC-powered units still make up a very large part of locomotive sales today.  These are conventional motors with carbon brushes that are a simpler technology than AC motors, though they are not quite as powerful and require more maintenance.

Dynamic Brakes: A system that uses the resistance of the locomotive's electric driving motors to help slow the train.  The train's movement forces the motors to spin, causing them to generate electricity.  This electricity is dissipated through grids in the roof of the unit, which are cooled by one or more fans.  Locomotives equipped with dynamic brakes (a common feature) usually have extra fans or air intakes in the middle or at the front of the hood.

Generator:  The generator is turned by the diesel engine and generates DC electricity, required to power the locomotive's traction motors.  Locomotives of the 1970s and later have alternators, which produce AC electricity and require less maintenance.

Horsepower: Amount of work a motor can do in a given amount of time (in other words, the amount of energy produced).
 
Prime Mover: Another term for the diesel engine inside the locomotive. Click here for more information.

Radial Truck: These are used on modern GE and EMD 6-axle units as well as the GE Genesis passenger units.  Radial refers to keeping the axle along the radius of a curve, which keeps each wheel exactly perpendicular to the rails on curvy track.  This enhances adhesion and reduces wheel and rail wear.  Older trucks relied on the broadness of the curve and play in the bearing assemblies to absorb the forces of a rigid truck frame.

Run: Any one of the eight positions of the throttle (as in "run 8" or full throttle).

Sander: A mechanism actuated automatically or manually that sprays sand in front of the locomotive wheels for better traction.  The sand doubles by not only providing additional adhesion, but the locomotive crushing it heats it up and will cause grease or moisture to dissipate, thereby further improving traction.  Locomotives used on mountain lines often have trucks covered in a layer of sand dust.

Starting Tractive Effort: Locomotive pulling power.  Starting tractive effort is how much a locomotive pulls from a standstill, and relates to how much traction is available.  More wheels and a greater locomotive weight generally means more starting tractive effort, in addition to the design of the trucks.  How much electric power is available is not as important, because too much would cause the wheels to slip.

Torque: Turning or twisting force of a motor.

Traction Motor: Powerful electric motor attached to each of the locomotive's axles to drive the train.
 
Truck: A locomotive or freight car wheel assembly.

A-unit: A locomotive with a cab.  This term has become less relevant since this is the only type of locomotive currently manufactured.

B-unit: A locomotive without a cab.  There is a small control room that allows the locomotive to be moved in yards and shops, but it cannot lead a train.
 
Consist: A group of connected locomotives.  Pronounced CON-sist; same meaning as "lash-up".
 
Coupler: Device that hooks train cars together.

Crossbuck: The X-shaped sign often accompanied by lights and a bell, and sometimes by gates, used to warn motorists of a railway crossing.
 
Ditch lights: Platform-mounted lights on the locomotive ends (often only on the front) that create the easily recognizable triangle of lights common to all North American trains.  Sometimes these lights flash alternatingly when the horn is blown.
 
Doublestack: A special well car carrying two containers stacked one on top of the other.

Helper: Radio-controlled locomotive or set of locomotives placed in the middle or at the rear of the train.  The use of helpers is done to prevent coupler failure in hilly terrain, where placing all locomotives at the front would create too much force on the couplers of the first few cars.

Horn: The proper term used to describe the device used for whistling at grade crossings. Click here for more information.
 
Hot-shot: A highly powered train relative to the amount of cargo.  This may mean up to 10 locomotives for a long but lightweight train such as a piggyback or container train.  A hot-shot may have more than 10 horsepower per ton (compared with 1 horsepower per ton on a typical drag freight).

Lash-up: A group of connected locomotives.  Same meaning as "consist".
 
Local: A small, short-distance freight generally under 20 cars in length.

MU (MU'ed): Short for "multiple unit"; describes how several locomotives can be controlled from a single cab by being connected electrically and pneumatically.

On the Point: The lead locomotive of a lash-up.
 
Pilot: Makes up the very front of the locomotive frame under the platform and goes to within a few inches above the rail.  Obscured by the coupler, air hoses and often a plow.  Positioned where the "cowcatcher" of steam locomotives used to be.

Slug: A locomotive with no diesel engine, which draws electrical power from the locomotive to which its connected.  The adjacent locomotive provides power for both its own traction motors and those of the slug, and must be modified to have extra electrical connections on the back to connect with the slug.  Slugs are used in low-speed conditions such as in yards or on drag freights, where tractive effort, not speed, is required.

Whistle: The sound created when blowing the horn; not to be confused with the horn itself.

Michael Eby 2005