Feedback is a process in which information about the past or the present influences the same phenomenon in the present or future. As part of a chain of cause and effect that forms a circuit or loop, the event is said to "feed back" into itself.
Ramaprasad (1983) defines feedback generally as "information about the gap between the actual level and the reference level of a system parameter which is used to alter the gap in some way", emphasising that the information by itself is not feedback unless translated into action.
"...'feedback' exists between two parts when each affects the other..."
Feedback is also a synonym for:
Feedback signal - the measurement of the actual level of the parameter of interest.
Feedback mechanism - the action or means used to subsequently modify the gap.
Feedback loop - the complete causal path that leads from the initial detection of the gap to the subsequent modification of the gap. Wikipedia, Feedback