Pareto-efficiency/Pareto-Koopmans efficiency:

Simply stated, a unit is Pareto-efficient when an attempt to improve on any of its inputs or outputs will adversely affect some other inputs or outputs. Formally, Chames et al (1981) consider a DMU to be 100% efficient only when ‘none of its inputs can be decreased without either (i) decreasing some of its outputs, or (ii) increasing some of its other inputs, and none of its outputs can be increased without either (i) increasing one or more of its inputs or (ii) decreasing some of its other outputs’. Since the condition for Pareto-efficiency is that a DMU’s efficiency score is 1, efficiency and Pareto-efficiency are synonymous. [Chames A, Cooper W W and Rhodes E (1981), ‘Evaluating program and managerial efficiency: an application of data envelopment analysis to program follow through’, Mgmt. Sci., 6, pp 668-697.]