Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to feed back into itself.

<electronics> Part of a system output presented at its input. Feedback may be unintended. When used as a design feature, the output is usually transformed by passive components which attenuate it in some manner; the result is then presented at the system input. Feedback is positive or negative, depending on the sign with which a positive change in the original input reappears after transformation. Negative feedback was invented by Black to stabilise vacuum tube amplifiers. The behaviour becomes largely a function of the feedback transformation and only minimally a function of factors such as transistor gain which are imperfectly known. Positive feedback can lead to instability; it finds wide application in the construction of oscillators. Feedback can be used to control a system, as in {feedback control}. (1996-01-02)

<electronics> A control system which monitors its effect on the system it is controlling and modifies its output accordingly. For example, a thermostat has two inputs: the desired temperature and the current temperature (the latter is the feedback). The output of the thermostat changes so as to try to equalise the two inputs. Computer disk drives use feedback control to position the read/write heads accurately on a recording track. Complex systems such as the human body contain many feedback systems that interact with each other; the homeostasis mechanisms that control body temperature and acidity are good examples. (1996-01-02)

Corrective feedback is a frequent practice in the field of learning and achievement. It typically involves a Learner receiving either formal or informal feedback on his or her understanding or performance on various tasks by an agent such as teacher, employer or peer(s).

Audio feedback (also known as acoustic feedback, simply as feedback) is a positive feedback situation which may occur when an acoustic path exists between an audio input (for example, a microphone or guitar pickup) and an audio output (for example, a loudspeaker). In this example, a signal received by the microphone is amplified and passed out of the loudspeaker.

In economics, economic value is a measure of the benefit provided by a good or service to an economic agent. It is generally measured through units of currency, and the interpretation is therefore "what is the maximum amount of money a specific actor is willing and able to pay for the good or service"?