Fuel economy, or fuel efficency, is used to describe how much fuel an engine/car consumes over time. Vehicles with better fuel economy can go further on a given amount of gasoline.
The distance a vehicle can go on one tank of fuel isn't a good measurement for comparing the fuel consumption of one vehicle to another, because some fuel tanks are larger than others.
If you are interested in improving the gas mileage of your own car, you can read how to do so on our dedicated article, How to Improve Fuel Efficency.