The following are links that you may use to create your definition of what fuel efficiency is. This is just a starting point for your research, if you cannot figure out your definition by using these sites, please look for more.
Why fuel Efficiency?
What's the Difference Between Fuel Efficiency and Fuel Economy?
Why is Fuel Economy Important?
Gasoline Vehicles: Learn More About the New Label
Fuel Efficiency
Why fuel Efficiency?
What's the Difference Between Fuel Efficiency and Fuel Economy?
Why is Fuel Economy Important?
Gasoline Vehicles: Learn More About the New Label
Fuel Efficiency