Focused improvement in theory of constraints is the ensemble of activities aimed at elevating the performance of any system, especially a business system, with respect to its goal by eliminating its constraints one by one and by not working on non-constraints.
The method to achieve focused improvement is the use of the five thinking processes.
Most of the popular performance improvement methods, such as TQM or reengineering, are not focused improvement methods, i.e. they do not distinguish working on the factors that limit a system's performance (constraints) — which brings immediate results, from working on non-constraints — which does not bring any results, only increases costs and distracts management's attention.
See also: Donella Meadows' twelve leverage points to intervene in a system