1. Feedback is the transmission of current or voltage from the output of a circuit or device back to the input, where it interacts with the input signal to modify operation of the device. Feedback is positive when it is in phase with the input, and is negative when it is out of phase.
2. To input the result at one point in a series of operations to another point; the method allows a system to monitor its actions and make necessary corrections.
See also, Positive Feedback, Negative Feedback