Hybrid
A vehicle propelled by a combination of power sources, such as a gasoline engine with electric motor assistance, to improve fuel economy and reduce emissions.
Hydrogen
The most abundant element in the universe.
Hydrogen vehicle
Some hydrogen vehicles burn hydrogen like gasoline, while others use is it to generate electricity via a fuel cell. Hydrogen fuel cell vehicles emit only water as “exhaust” and are considered zero emissions vehicles.
Hypermiling
The “sport” of maximizing fuel economy via techniques (many of them not recommended) such as turning off the engine while coasting, driving behind large vehicles to reduce or eliminate wind resistance, etc.