Green Car Glossary: Vehicles, Drivetrains, Emissions, Fuels, Energy

As gasoline prices go up, acronyms like EREV, CNG, and MPGe are becoming more and more common.
Ever wonder what they all mean?
Here's your chance to enter a veritable Twilight Zoneof terminology--and find out, say, whether a PZEV is related to a PHEV.
(It's not.)
To help you in your journey, our glossary is divided into categories: Vehicle Types, Drivetrains, Emissions, Fuels, and Energy Storage.
This glossary is by no means comprehensive as new acronyms seem to appear on a daily basis.
Think of it as a starting point, and feel free to add comments about terms we may have missed.
VEHICLE TYPES
BEV - Battery Electric Vehicle. A BEV is not a hybrid; it does not have an internal combustion engine (or ICE) and it relies solely on electric power, supplied by a battery pack. Because BEVs aren't powered by gas, they have zero emissions. The biggest drawback to pure electric vehicles is their limited range. Typical BEVs have a range of 70 to 100 miles. The Tesla Model S is an exception, with its two versions offering EPA-rated driving ranges of 208 miles or, for the pricier model, 265 miles per charge.
The range of battery-electric vehicles can be dramatically affected by the weather--cold weather in particular. Most BEV manufacturers have built in heaters that warm the battery while the car is being charged.
HEV or HV - Hybrid Electric Vehicle or Hybrid Vehicle. Whether HEV or HV, it's a hybrid--a car or truck with a standard gasoline-powered engine that also has a high-voltage battery and an electric motor, both of which supply additional power to the vehicle's drivetrain. All hybrids share the goal of reducing the amount of gasoline used by the vehicle and lowering its emissions, but they tend to go about it in different ways. The Toyota Prius is currently the highest-selling (and probably best-known) hybrid vehicle.
Mild Hybrid - This is a type of hybrid that cannot be driven on electric power alone, even for a short distance. Almost every Honda hybrids to date has been a mild hybrid, though that is changing for 2014 with the addition of the Accord Hybrid and Accord Plug-In Hybrid. Mild hybrids have only one electric motor-generator; "full hybrids" may have one (Audi, BMW, Hyundai, Kia, Mercedes-Benz, Volkswagen, and others) or two (Ford, Honda, Toyota).

PHEV or PHV - Plug-in Hybrid Electric Vehicle or Plug-In Hybrid Vehicle. PHEVs are conventional hybrids that have been modified by enlarging their battery packs and adding the ability to recharge those batteries by plugging them into wall current. Today, plug-in hybrids are offered by Ford, Honda, and Toyota, and there will likely be several more in future model years. Plug-in hybrids have rated ranges of 6 to 21 miles on electric power only (under gentler conditions than most drivers today may be used to). Once their battery packs are depleted, they revert to operating like regular hybrid cars.
EREV - Extended-Range Electric Vehicle. There is great debate in the field about whether a range-extended electric vehicle should be grouped in the category of plug-in hybrids or considered to be its own type.
Unlike PHEVs, which may switch on their engine at any point if power demand is high, an EREV stays all-electric under every circumstance until its battery is depleted. Then its engine switches on to run a generator that provides energy to turn the wheels.The best-known EREV is the Chevrolet Volt; the only other such car offered for sale was the 2012 Fisker Karma, of which about 2,500 were sold before that company ended production.
DRIVETRAINS
Hybrid vehicles generally use one of three different methods for supplying power to the wheels.
BAS - Belt Alternator/Starter - A parallel system used by mild hybrids that provides some fuel savings (not as much as a full hybrid) at a relatively low cost. BAS systems use a large alternator connected by a serpentine belt to the crankshaft. This allows the gas engine to stop and then quickly restart (at stop lights for example) and also provides some assistance to the gas engine for moving the car. Now in its second generation and rebranded as eAssist, it's used exclusively by General Motors in Buick and Chevrolet sedans.