System Optimization is a holistic technical approach to energy efficiency that focuses on the efficiency of the whole system rather than focusing on individual components.
For example, a factory might take the decision of buying a more efficient pump to improve its energy efficiency but the “real” energy saving opportunities might lie in the piping system or control system of the pump rather than the pump itself.
In addition, it focuses on designing for efficiency. Following the same example the pump that the factory has decided to replace might have been over-designed in the first place, i.e. the engineering department has designed the system to accommodate future increases in production that might not take place until several years to come.