ef·fi·cien·cy 
(ĭ-fĭshən-sē)
(ĭ-fĭshən-sē)n. pl. ef·fi·cien·cies
1.
a. The quality or property of being efficient.
b. The degree to which this quality is exercised: The program was implemented with great efficiency and speed.
2.
a. The ratio of the effective or useful output to the total input in any system.
b. The ratio of the energy delivered by a machine to the energy supplied for its operation.
3. An efficiency apartment.