* HEVs (hybrid electric vehicles): Hybrids combine an internal combustion engine with a battery and electric motor, offering the extended range and rapid refueling of a conventional vehicle but with the potential for much higher fuel economy. However, not all hybrids are created equal; some use the technology to increase acceleration rather than boost gas mileage. The UCS Hybrid Center website provides information about and comparisons of current hybrid models.
* FFVs (flex-fuel vehicles): FFVs have a single fuel tank, fuel system, and engine, but are designed to run on any blend of gasoline and ethanol, up to 85 percent ethanol (a mixture known as E85 that can modestly reduce a vehicle’s global warming emissions such as carbon dioxide). Unfortunately, E85 fueling stations are not available in all states; check the Department of Energy’s Alternative Fuel Station Locator for a list of stations nearest you.
* NGVs (natural gas vehicles): Honda is currently the only automaker offering passenger cars that run on compressed natural gas (CNG). CNG emits less air pollution and carbon dioxide than gasoline, but as with E85, CNG fueling stations are not widespread.
To which we would add: PHEV (plug-in hybrid electric vehicles) for hybrid vehicles that can be plugged-in to recharge their batteries. These usually have a longer electric range than regular hybrids which allows them to take short trips on electricity only.
And EV (electric vehicles): Vehicles that are powered by electricity only. Usually referring to cars with batteries (like the Tesla Roadster) and not hydrogen fuel cells (which are also electric cars but referred to as FCVs, Fuel Cell Vehicles). Their main benefit is that there is already a refueling infrastructure (the power grid) and that electricity can be produced a large number of ways, including clean ones. Their main weakness is battery technology limitations (capacity, cold weather, cost).
* VVT (variable valve timing) or VVLT (variable valve lift and timing) adjusts the operation of an engine’s valves depending on engine speed and power demand. By providing a better fuel/air mix and improved combustion, these technologies boost fuel efficiency.
* AFM (Active Fuel Management), MDS (Multiple Displacement System), and VCM (Variable Cylinder Management) are brand names used by General Motors, DaimlerChrysler, and Honda, respectively, to describe their cylinder deactivation systems, which shut down half of an engine’s cylinders when the extra power is not needed. This is particularly useful for vehicles with six- and eight-cylinder engines.
* CVT (continuously variable transmission) is an automatic transmission with an essentially infinite number of speeds, which enables the engine to operate near its optimal speed under all conditions.
CVT is an interesting technology. You can learn more about how it works here. It's too bad that it is not as popular in North-America as in the rest of the world because it doesn't have that "shifting" feel that a traditional automatic transmission has.