Learner's definition of EFFICIENCY
1 : the ability to do something or produce something without wasting materials, time, or energy : the quality or degree of being efficient
Because of her efficiency, we got all the work done in a few hours.
The factory was operating at peak efficiency.
a car with greater fuel efficiency [=a car that uses fuel more efficiently]
A furnace with 80 percent fuel efficiency wastes 20 percent of its fuel.