Efficiency is a measure of how well resources are converted into output: less cost, time, or effort per unit produced. It is the discipline of "doing things right," optimizing a given activity so it consumes fewer inputs for the same result.
Efficiency says nothing about whether the activity should be happening at all. Improving the efficiency of an initiative that should not exist simply produces the wrong result more cheaply — which is why efficiency is only valuable once effectiveness has settled the question of whether the work is the right work.
