Feedback/Feedback loop
In a system – mechanical, electrical, biological, or informational, etc. – in which some input or cause gives rise to some output or effect, feedback is that part of the output which is returned or directed back to the input, influencing and modifying the behaviour of the system. For example, a room with a heater operating fitted with a thermostat set at a particular temperature, the heater will work to produce the required amount of heat to maintain the room at that temperature (with some relatively small range of fluctuation) involves a feedback loop. A second somewhat different example would be the case in which an author asks for reviewer comment for the first draft of a piece of writing, with a view that a subsequent draft or drafts can be modified in light of the feedback received.

In biological systems the production of a hormone often stimulates a process which in turn inhibits the production of this same hormone and so finely regulating the amount of the hormone present, for example, in relation to blood sugar concentration.