Her are few terms:
* ALCOholic: a railfan who loves, or is obsessed with, American Locomotive Company (ALCO) locomotives.
* Alligator: ALCO RSD-15 locomotive, so named for its long, low nose.
* B-Boat: GE B23-7, B30-7 or B36-7 locomotive. By analogy with U-boat, since with the Dash 7 line, the "B" or "C" moved to the beginning of the designation.
* B-Unit: A booster locomotive commonly with no cab.
* Baby Boat: GE U18B locomotive.
* Baby Tunnel Motor: EMD GP15-1 or GP15T locomotive, so-called because its low air intakes resemble those of the much larger SD40T-2 and SD45T-2.
* Bandit: Nickname for Milwaukee Road engines after the railroad was sold to the Soo Line. The Soo covered up the Milwaukee Road name and logo on the orange locomotives with black paint, causing them to resemble bandits.
* Baretables: Empty flat, spine or well cars.
* Basketball: Nickname for the Pan Am Railways logo.
* Big G, the: Nickname for Guilford Rail System, in reference to the large "G" emblem on their locomotives and boxcars.
* Big Mac: Nickname given to EMD's SD70MAC, SD80MAC and SD90MAC locomotive models.
* Billboard: Santa Fe locomotive in the pre-1972 blue and yellow scheme
* Black Widow: Southern Pacific Locomotive (All black with some silver)
* Bloody Nose: Southern Pacific Locomotive (Post 1959, grey and red paint scheme)
* Blowdryer: Nickname for dynamic brakes.
* Bluebonnet: one of two Santa Fe paint schemes. The standard freight scheme from 1972 until the BNSF merger was dark blue with yellow on the front, with the same color division as the warbonnet scheme. It is also known as Yellowbonnet. Bluebonnet can also mean a warbonnet unit with only the red painted over, resulting in a silver and blue locomotive; this was used on passenger engines transferred to freight service after the formation of Amtrak.
* Baobab: (PRR only): an oversize load. From the telegraph code-word used. A baobab tree is a very large tropical tree.
* Booster: (Diesel locomotive) - a cabless B unit or Slug. Although a Slug and a B Unit differ slightly, (See related articles for details) both serve the same purpose of adding more tractive effort.
* Brick: GE E44 electric engines used by Pennsylvania, Penn Central and Conrail (called this because the road-switcher style engines were as ugly as a brick compared to the classic PRR GG1s that they worked along side of)
* Bright Future: The middle CSX tricolor paint scheme (also known as Yellow Nose 2 or YN2).
* Buggy: a caboose on the Boston and Maine Railroad.
* Bull: a railroad police officer.
* Butthead: Switching locomotive with the operating cab located at the rear end of the carbody.
* Cabbage: Former F40PH locos with the diesel engine removed, and a roll-up baggage door installed in the center of the carbody; used as cab/baggage cars in Amtrak push-pull service.
* Cadillac: A nickname for EMD SD9 locomotives, in reference to their smooth ride quality reminiscent of a Cadillac automobile. This nickname is said to have originated on the Southern Pacific Railroad.
* Calf: A cabless switcher. Not a slug; it has its own diesel engine.
* Can Opener: Conrail's herald
* Catfish: Norfolk Southern's D9-40CW locomotives.
* Ches-C: Chessie System's kitten logo.
* Chicken Bone: Amtrak's City of New Orleans
* Coal Drag: A train loaded with coal.
* Covered wagon: an EMD E-series or F-series locomotive.
* Cow: a switcher locomotive, when paired with a Calf.
* CPLs: Color Position Lights, PRR style signal heads with new color lenses installed.
* Crap-9: Another term of derision for Dash-9 engines.
* Crash 8: A term for CSX's C40-8Ws that are starting to show their age.
* Critter: A small industrial locomotive.
* Dark Future: The current CSX paint scheme (also known as Yellow Nose 3 (YN3) or Gold Nose 1 (GN1)).
* Darth Vader: Term used to describe the lens hood on a modern style of railroad signals, due to its visual resemblance to the helmet of Darth Vader from Star Wars. 
* Deathstar: Term used to describe the logo of the Illinois Central, which has the letter "i" inside a circle — based on a resemblance to the Death Star battle station in Star Wars.
* Diamond/Diamonds: Level crossing of two railroad tracks, at any angle from 15° to 90°.
* Diet Pepsi: An Amtrak GE Dash 8-32BWH wearing the Phase IV paint scheme. (See Pepsi Can)
* Dinky: Nickname given to small locomotives, particularly while in industrial service.
* Dirt Dauber: Loaded phosphate train.
* Douche-9: Another term of derision for Dash-9 engines.
* Draper-Taper: Canadian National units with wide/extended hoods
* Dress Blues: Former Conrail unit, nostalgic.
* Dump Truck: a GE AC6000CW, based at least partially on the fact that these units are almost always covered with dirt and grime.
* Dynamics/dynamic braking: Regenerative braking in which the motors on the locomotive wheels generate electric power off of the momentum of the moving train, and this power is burned off through resistor grids as heat.
* Elephant-style: A lashup of multiple locomotives with all units facing forward
* Ex-Con: Former Conrail unit or former Conrail employee
* Fallen flag: a railroad company that no longer operates.
* Wings/Flags/Flares (W/F/F): Characteristics used to designate Union Pacific's paint scheme and engine type. Wings = "Wing" Decal on the engine nose, Flags = "American Flag" Decal on engine body, Flares = "Flared Radiators" of certain SD70Ms on the long hood. Some engines have one or more of these UP characteristics.
* Fatheads: Wide-nose (North American Cab) locomotives.
* Firework Show: Nickname for the sparks that shoot out from the electrified third rail when a train passes over it when the rail is damp.
* FRED: "Flashing Rear End Device" located on the rear of trains, measures train air line pressure and train speed
* Foamer: a railfan, particularly one whose enthusiasm is excessive, or one who has a particular interest in steam locomotives.
* Ford Edsel: Amtrak GE Genesis locomotives.
* Furball/Furbie: Locomotive owned by First Union Rail (FURX).
* FRN: an acronym for "fucking rail nut", a derogatory term used by some railroaders to describe railfans.
* Geep: Nickname for EMD's GP series of locomotives
* Gennie: A MetroNorth or Amtrak GE P32AC-DM locomotive.
* Genset: A switching locomotive that uses two or three high-speed diesel engines, rather than one medium-speed diesel engine. Sometimes confused with Green Goat locomotives; the only similarities between the two types are their outward appearance and that both are designed to reduce air pollution.
* GEVO: Nickname for GE Evolution Series locomotives, in reference to the GEVO-12 engine used in those units.
* GN1: Gold Nose 1, the current CSX paint scheme. Another term for YN3.
* Goat: a locomotive used in yard switching service.
* Green Goat: A type of "hybrid" switching locomotive utilizing a small diesel engine and a large bank of rechargeable batteries.
* Greenie Weenie: Leased locomotive, typically of Burlington Northern heritage.
* Guilford Fail System: Guilford Rail System (derogative). Several Guilford locomotives have had the "R" in the word "Rail" vandalized to resemble an "F," thus resulting in this nickname.
* Hammerhead: A Dash-8 or Dash-9 series locomotive running long hood forward.
* Hertz: A locomotive leasing company.
* High Ball: Another term for a clear signal, derived from the days of steam where a station operator would hoist a ball up the scaffold, signalling the engineer he was authorized to proceed.
* Hogger: locomotive engineer.
* Horsehead: Norfolk Southern's new locomotive livery with a horse's head embedded in the NS Logo. (sometimes also called 'Mr. Ed')
* Hotbox: Overheated wheel bearing.
* Iron Triangle (The): An area near downtown Fostoria in northwest Ohio where two main lines of CSX Transportation (the former Baltimore and Ohio line between Akron and Chicago and the former Chesapeake and Ohio Railway line between Columbus and Toledo) and one main line of Norfolk Southern (the former Nickel Plate Road line between Bellevue and Fort Wayne) cross each other in close proximity.
* Jenny (also Jimmy): A 24 ft or 25 ft long ore car. Also refers to mine gondolas, as well as gondolas and hoppers from the early days of railroading.
* Jet: New Haven EP-5 electric locomotive, named for its loud cooling air blower equipment.
* Juice jack: Electric locomotive.
* Juice Train: Unit train of Tropicana cars.
* Junk box: see Rent-a-Wreck.
* Kodachrome: Southern Pacific Santa Fe Railroad's red, yellow and black paint scheme, which resembled the packaging of Kodachrome color transparency film. This was the scheme instituted when the merger between Southern Pacific and Santa Fe was assumed to be approved. Hundreds of locomotives were painted in Kodachrome colors before the merger was denied.
* Lightning Slinger: telegraph operator.
* Manifest: A freight train with a mixture of car types and cargos.
* Mate: See Mother.
* Mating Worms: Penn Central logo
* Meatball/Swedish Meatball: Amtrak EMD AEM-7 / ABB ALP-44 electric locomotives; so named for their design being based on the Swedish Rc4.
* Miniquad: Four ore cars (jennies) permanently coupled.
* Monobrow: The second version of Norfolk Southern's "Horsehead" paint scheme
* Mop, the: the Missouri Pacific Railroad (MoPac).
* Mother: The locomotive that is paired with a slug.
* Mud Missile: Derogatory nickname given to GE Genesis locomotives, in reference to their involvement in the 1993 Big Bayou Canot train disaster.
* Nuetered Stallion: A term given by Norfolk Southern's employees for the new horsehead logo.
* Orange: One of Tropicana Orange Juice Company's Bright Orange boxcars.
* Pac-Man: A nickname for Canadian Pacific Railway's 1968-1996 logo featuring a black triangle within a white half-circle, which resembles the main character of the video arcade game Pac-Man. It was CP's corporate logo for all business aspects - railway (CP Rail), shipping (CP Ships), telecommunications (CNCP), trucking (CP Express) and airline (CP Air).
* Patch: A locomotive wearing a new reporting mark and/or number on a "patch" over existing paint, usually of the former owner's.
* Pennsy Style: Nickname for old Pennsylvania Railroad position light signals
* Pepsi Can: An Amtrak GE Dash 8-32BWH, in reference to the units' original paint scheme with large red and blue stripes.
* Pig train: a train devoted exclusively to intermodal traffic, generally trailers on flatcars (TOFC) or containers on flatcars (COFC).
* Private varnish/PV: privately owned passenger cars.
* Pumpkin: BNSF Railway's current paint scheme, CSX's maintenance-of-way paint scheme. Formerly also ICG's all-orange scheme.
* Racetrack: Nickname for a stretch of Metra Commuter Rail line and BNSF freight line between Chicago and Aurora, Illinois where commuter trains and freight trains commonly attain high speeds.
* Racks: Nickname for autorack cars
* Raccoon: Norfolk Southern locomotives that have the entire area around the cab windows painted white, resembling the face of a raccoon.
* Railfan Window: The window in the end door of the lead or last car on a subway train or commuter train without a full-width cab.
* Rare Mileage: A passenger train traveling over track that does not have regular passenger service.
* Red Barns: Canadian Pacific's SD40-2F locomotives
* Rent-a-Wreck: Locomotive owned by a leasing company
* Roster Shooter: Someone interested in shooting every locomotive road number they can.
* Royal Toaster: Nickname for the Amtrak AEM-7 #946 that led a train carrying Prince Charles and the Duchess of Cornwall.
* Screamer: EMD F40PH locomotive, in reference to it operating in a constant state of full throttle (in order to provide head-end power to passenger cars). Coined by MBTA railfans.
* Screaming Thunderbox: EMD F40PH locomotive, particularly while in Amtrak service.
* Sergeant Stripes: a Canadian National locomotive in the 1970s-1980s paint scheme featuring light grey stripes on the locomotive's long hood.
* Shower Caps: Canvas coverings which protect the mouths of locomotive air horns on most freight units. Usually blue in color, and easily deteriorated by exposure to the elements.
* Silver Snake: Name given to Norfolk Southern's PPLX hopper trains which have only silver Bethgon hoppers
* Slug: A locomotive, with or without an operator's cab, which lacks a diesel engine, and draws power for its traction motors from a normal locomotive, known as a "mate" or "mother."
* Slushbucket: SD26 locomotive. So named for their muffled-sounding turbochargers.
* Snow Cones: Stainless steel coverings which protect the mouths of locomotive air horns, particularly on passenger units such as those used on Amtrak. So called due to their shape, which helps to deflect debris while at speed.
* Speeder: a small, motorized track inspection vehicle. Also called motorcar, trackcar, putt-putt, or golf cart.
* Space Age Noodle: Another name for the current Canadian National logo.
* Speedo: a track speed restriction (slow order).
* Spin Cycle: derogatory name for the compressor noises made by GE D9-40CW locomotives when idling.
* Stacks: Nickname for double-stack cars or trains
* Stealth Unit: The early CSX grey & blue paint scheme. So named for their virtual invisibility in poor light. Also used to describe NS D9-40CWs in light gray primer paint, and a scheme used on some Metro-North locomotives.
* Susie-Q: Nickname for the New York, Susquehanna & Western Railroad.
* T-Hog: Nickname for a Reading Railroad T-1 4-8-4 steam locomotive.
* Taco Belle: Nickname for the new Southern Belle-inspired paint scheme on Kansas City Southern Railway locomotives.
* Toaster: Amtrak AEM-7/ALP-44 or GE P42DC locomotives. Also used to refer to any GE locomotive, due both to their tendency to shoot flames out of the exhaust stack during Turbo Lag and to General Electric's historic involvement in the manufacture of household appliances.
* Tomato Can: M2 (railcar) operated by Metro-North Railroad.
* Tri-Color: type of signal which features red, yellow, and green in a triangle shape
* Tunnel Motor: Southern Pacific EMD SD40T-2 / EMD SD45T-2. Named for the lower-located air intakes to prevent the locomotive from pulling diesel exhaust in with the clean air while traveling through a tunnel.
* Turbo Lag: Characteristic of older Alco locomotives (and in more modern times, GE locomotives), where the turbocharger lags behind the throttle-up of the diesel, shooting dense clouds of black smoke and/or flames from the exhaust stack when initially throttling up.
* U-Boat: GE Universal Series locomotive.
* Vomit Bonnet: BNSF's first attempt at a paint scheme
* Warbonnet: Santa Fe's red and silver paint scheme (less common since the BNSF Railway merger in 1995)
* Warpumpkin: Name given to the BNSF orange and black update of the classic Sante Fe Warbonnet scheme.
* Washboards: name given to M.U. cars, subway cars, and other equipment made with corrugated side panels that resembled washboards.
* Wet Noodle: Canadian National's stylized CN logo, in use since 1961.
* Whiteface: first version of Norfolk Southern's "Horsehead" paint scheme. Paint scheme used on Burlington Northern's widecab SD60s
* Window train: a passenger train.
* Winnebago: Nickname for Metra's fleet of EMD F40PHM-2 locomotives, in reference to that model's resemblance to the popular recreational vehicle.
* Worms In Love: Nickname for Penn Central's herald. Commonly known as "mating worms."
* Yellowbonnet: one of two Santa Fe paint schemes. The standard freight scheme from 1972 until the BNSF merger was dark blue with yellow on the front, with the same color division as the warbonnet scheme. It is also known as Bluebonnet. Yellowbonnet can also mean a warbonnet unit with only the red painted over, resulting in a silver and yellow locomotive; this was used on passenger engines transferred to freight service after the formation of Amtrak.
* YN1: CSX's first yellow-nose paint scheme; gray overall with dark blue on the top half of the cab and yellow on the front of the nose; blue "CSX" lettering
* YN2: CSX's second yellow-nose paint scheme; more yellow on the nose; the whole cab is dark blue, along with a stripe on the side; blue or yellow "CSX" lettering
* YN3: CSX's third yellow-nose paint scheme; dark blue overall with a yellow nose; yellow "CSX" lettering
* Zebra Stripes: A Santa Fe locomotive in the early black scheme with white warning stripes
courtesy of spottingworld.com