A closed system is a system which relies on a feedback loop to control its output in a control system in systems theory. (It is sometimes called "closed-loop system.") The system is a "closed" system because it is closed by a feedback loop in its control, as opposed to an open system where there is no feedback loop in its system. In a closed system, part of the output of this system is also used as the input to the system, which is essentially its "feedback." System (from the Latin (systēma), and this from the Greek (sustēma)) is an assemblage of entity/objects, real or abstract, comprising a whole with each and every component/element interacting or related to another one. ... In cybernetics and control theory, feedback is a process whereby some proportion or in general, function, of the output signal of a system is passed (fed back) to the input. ... It has been suggested that this article or section be merged with Control theory. ... Systems theory is an interdisciplinary/multiperspectual field of inquiry that studies the theoretical and actual properties of systems as a process by looking at it in terms of relationships from which emerge new properties of wholes. ...

A closed system can rely on a positive feedback or a negative feedback or both in its control operation. In contrast, an open system is a feedforward system that does not rely on feedback for its control function. Positive feedback is a feedback system in which the system responds to the perturbation in the same direction as the perturbation (It is sometimes referred to as cumulative causation). ... Negative feedback is the process of feeding back to the input a part of a systems output, so as to reverse the direction of change of the output. ... Feed-forward is a term describing a kind of system which reacts to changes in its environment, usually to maintain some desired state of the system. ...