Efficiency n. : The quality of being efficient or producing an effect or effects; efficient power; effectual agency.

Efficiency n. : The ratio of useful work to energy expended.

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Taxonomy
Efficiency, free encyclopedia, energy, measure, fuel efficiency, Pareto efficiency, thermodynamics, science and technology, economics, search, free dictionary, physics, desirability, estimator, optimizing, speed, memory requirements, computer program.

Defination from the web:
efficiency, how efficient is the trading going on the financial markets ... Business efficiency, expenses as a percentage of revenue, etc. ... Energy conversion efficiency, desired energy output per energy input. Energy conservation, reducing the use of energy ...