M & S: Acronym for "mud and snow," as in M+S tire. A tire with a tread design which gives the maximum traction in mud and snow.
machining: an operation which shapes metal parts by carving away excess material as chips produced in a sequential process of turning, milling and grinding operations.
Mag: [1] Abbreviation for "magneto."
[2] Abbreviation for "magnesium," as in mag wheels."
Magnaflux: A special chemical process, used to check parts for cracks.
Magnesium Wheel: An alloy wheel.
Magnet: A piece of magnetized steel that will attract all ferrous material. The permanent magnet does not need electricity to function and will retain its magnetism over a period of years. Often shaped into the letter "U."
Magnetic Clutch: A coupling device used to turn the compressor off and on electrically.
Magnetized:

made magnetic

Magneto: An electrical device which generates electrical current when it is rotated by an outside source of power. It needs no outside source of power such as a battery. It may produce either low or high tension current.
Magneto Ignition: A compact assembly of a magneto generator, an ignition coil, and a distributor. Ignition voltage is induced within the magneto by the movement of a coil relative to the poles of a permanent magnet. Because it needs no battery, the system is particularly suited for small engines, e.g., motorcycles, outboard engines, etc.
Magneto Puller: A tool which screws into the center of the magneto to force the magneto away from the shaft on which it rides.
Make: the company who built the car. For example - Lincoln, Mercury, Pontiac, Chevrolet, Dodge, Plymouth, Buick, etc.
Main Beam: (Br) high beam
Main bearing: The bearings in the engine block that support the crankshaft.
Main Sun Visor: In dual visor systems, the main visor is moved sideways and the secondary visor is flipped down, thus shielding the driver from the sun from both the front and side
Maintenance: The work undertaken by a car owner to keep his vehicle in good working order; typically checking the tires, lights, oil and coolant levels, windscreen wipers, and seat belts.
Maintenance Free: Something that requiring no work in order to be kept operational
maintenance-free battery: A battery with a permanently sealed top, thus requiring no topping-up
maintenance manual: A book of instructions detailing routine maintenance
Make: brand name of a car or truck (i.e., Chevrolet, Ford, Dodge, Honda).
Malfunction: Problem in system that affects normal operation
Man: Short form for manual transmission
Maneuver: to drive or steer a vehicle around obstacles or in a confined space
maneuverability: The ease with which a vehicle can be steered around objects
Manifold: A pipe or number of pipes connecting a series of holes or outlets to a common opening.
Manifold Heater: A system used to improve the cold start behavior of an engine, consisting of heating ducts incorporated into the intake manifold that are connected to the water cooling system of the engine; alternatively, an electric heater may be used.
Manual: [1] Something done by hand.
[2] A colloquial term for a vehicle with manual transmission.
[3] A book of instruction.
Manual Choke: A linkage system which begins with a knob on the dash which can be pulled to activate and pushed to de-activate. The knob is attached to a cable and the other end of the cable is attached to a the butterfly valve on the carburetor. Because many drivers had difficulty knowing when to use the choke knob, manufacturers developed the automatic choke system which decides this information for the driver.
Manually Operated window: window operated by turning a lever by hand. Compare electric window
Manual Steering: A steering system that does not have a power booster to reduce the effort of steering changes especially during slow movements such as parallel parking.
manual transmission: A transmission system in which gears are selected by the driver by means of a hand-operated gearshift and a foot-operated clutch. In a motorcycle the clutch is hand-operated and the gearshift is foot-operated. Contrasts with an automatic transmission. Also called a "standard transmission."
manufacturer's suggested retail price: (MSRP) The suggested retail price the dealer is asking. Generally the same as the "sticker price." Dealers typically sell at a discount to this price.
Map Light: An interior light to facilitate, for example, map reading.
Marker Lights: the lights mounted on the fenders of a car that mark its outside boundaries and corners.
Marque: (Fr) (pronounced "Mark") a particular make or brand of car. Also spelled "marquee"
Masking Tape: An adhesive tape used to cover surfaces that border an area to be painted, so as to protect them
master cylinder: holds the brake fluid for a disc brake system
Mass-produced car: A car which is manufactured in great numbers to a standard pattern and with extensive mechanization
Mass transit system: A system designed to transport large numbers of people or goods
Mechanic: A person who works on engines or machines.
Mechanics lien: When you take your vehicle to a shop to be repaired and you fail to pay your repair bill, the repair shop has a lien on your vehicle and can confiscate and sell your vehicle to pay for the work on your vehicle.
memory button: A button which operates the position of electric seats, mirrors, etc. and which stores the requirements of a particular driver in its memory
Mesh: to engage, especially gears. The opposite is disengage
metallic Paint: A finish paint colors that contain both pigment and small metallic flakes which reflect light. The opposite is solid paint. The flakes are often of different sizes. When the surface is viewed from different angles, the color shade seems to vary, since the flakes are all oriented at different angles in the paint and consequently reflect the light differently.
Mickey mouse A trivial thing. In automotive usage it means something that is simplistic and worthless.
Micocar: small car, popular in the 1950s, that featured a body offering full-weather protection and mechanics often derived from motorcycle technology, e.g., Goggomobil, BMW Isetta, etc.
Minibus: small, single-decker bus designed to carry around 12-20 people
Minicar: A very small sedan carrying no more than four adults
Minivan: [1] minibus-sized van with no side windows, used to transport goods instead of people.
[2] A smaller van, with windows, which became popular with the VW van and its GM copy Greenbrier (based on the Corvair). Later, Chrysler produced its Magic Wagon series (also copied by GM and Ford) which has almost eliminated the station wagon.
Mint Condition: A colloquial term for a vehicle that has been kept in, or restored to, perfect condition. Also called "cherry condition."
Mirror: A reflective device which is located in one of several positions: between the two A-posts within the passenger compartment (called the rearview mirror); behind either/both sunvisors (vanity mirror); on either side of the outer A-posts; on the forward or leading edge of the front doors; or on the front fenders.
Misfire: The failure of the fuel charge in one or more engine cylinders to fire or ignite at the proper time. It can be due to poor compression caused by worn or improperly adjusted valves, worn piston rings, a faulty head gasket, or in the case of a two-stroke engine leaking crank seals. It can also be caused by poor ignition due to worn or dirty spark plugelectrodes, worn or improperly gapped points or spark plugs, poor fuel delivery, faulty ignition wiring, or faulty distributor components. An easy way to detect the problem is to put a stiff piece of paper at the end of the tail pipe and listening for an irregular puffing sound. Also called "missing" or "backfiring."
Misfiring: Failure of an explosive to occur in one or more cylinders while engine is running. This may be a continuous or intermittent failure
Mist Action: An action of intermittent wipers which will make one or two swipes to clear away any mist from the windshield.
mobile home: A large home which can be hauled to its location (it does not have an engine). Once in place, the wheels are removed. In most cases, the home is never moved again. A motor home, in contrast, keeps its wheels and has its own engine.
Mock-up: A full-size model of a vehicle made of wood and clay, used for design studies.
 Model: the name of the car. For example, Sable, Continental, Grand Am, etc.
Model year: (MY) A new model year starts after the summer break of the car production plant, during which the assembly lines are altered to accommodate the changes introduced in the cars of the next model year. A model year and year of manufacture can, therefore, differ.
 Monochromatic Taillights taillights that have a red brake/turn signal lens. Usually found on American cars. See taillights.
Monster: A type of vehicle, usually a truck, which has very large tires.
Monthly Payment: [1] The amount that must be paid each month to satisfy the lease contract. It is common for the monthly payment shown in lease advertisements to exclude applicable taxes, which will add to the amount paid each month.
[2] The amount that is paid on a vehicle loan.
Mopar: Trade name of Chrysler Corp for its motor parts (i.e., MOtorPARts). Chrysler also uses the name Autopar to indicate its automobile parts (i.e., AUTOmobilePARts).
Moped: A two-wheeled motorized bicycle (short for motorized pedal bicycle) with an engine of less than 50cc
Mother-in-law Seat a single seat attached to the back of a two seater car, the forerunner of the rumble seat. It can also denote a seat placed on the opposite side of the car from the driver
Motor Car: (Br) A British term for a car or automobile (a 4-wheel road vehicle)
Motor Caravan: (Br) A British term for motor home
Motorcycle: A two-wheeled motorized vehicle where the two wheels are not side-by-side but in line. Most have the fuel tank ahead of the saddle and the engine just below the tank. The engine size usually ranges from 50cc to 1500cc. Also called "motorbike" or just "bike."
Motorhome: A motorized recreational vehicle that looks something like a bus.
Motorist: Someone who drives an automobile
Motorized: A wheeled vehicle with a motor or engine.
Motor Oil: engine oil or gear oil
Motor Vehicle: Any automotive vehicle that does not run on rails; usually with rubber tires; such as cars, vans, trucks, lorries, scooters, and motorcycles
Motor Vehicle Safety Act: (MVSA) Act which regulates the manufacture and importation of motor vehicles and motor vehicle equipment to reduce risk of death, injury and damage to property and the environment.
Motor Scooter:  A lightweight motorcycle with small wheels, an enclosed engine, open foot platform, and leg shields. Also called "scooter."
Motorway: A multi-lane, main road for fast-moving traffic with speed from 55 mph to 70 mph (90 - 110 kph) with a center median, and few exit and entry points
MPG  Abbreviation for "miles per gallon," as a measure of fuel consumption. The U.S. gallon is 3.785 liters. The Imperial gallon is 20% larger (4.546 liters). When a vehicle gets 30 mpg (US), he will get 36 mpg (Imperial). The metric system calculates fuel consumption as the number of liters per 100 kilometers. The same vehicle will be giving 7.8 l/100 km.
mPH: Abbreviation for "miles per hour." The metric equivalent is Kilometers per hour (kph). To convert Miles to Kilometers, multiply by 1.609344. It may be easier to divide the miles by 10 (i.e., knock off a zero) and then double it four times. Thus 60 mph divided by 10 is 6. Doubled is 12, doubled is 24, doubled is 48, doubled is 96. The accurate figure is 96.56, but 96 is probably close enough. To convert from Kilometers to Miles, divide by 1.609344. It may be easier to multiply is by 10, then chop it in half four times. Thus 70 kilometers becomes 700. Chopped in half it is 350, chopped again is 175, again is 87, and one more time is 43.5. Accurately it is 43.49.
Mud Flap: A rubber or plastic shield which is positioned behind a wheel (usually the rear wheels) to prevent mud and small rocks from being thrown up against the body of the vehicle or from being thrown at a following vehicle. Also called "splash guard"
muffler a part of the exhaust system that eliminates noise
Muffler-cut-out a valve located on the exhaust pipe between the engine and the muffler. When opened it allowed exhaust gas to pass directly to the open air which made a great noise and slightly increased power
Muscle Car a stock vehicle with greater than usual horsepower