Merriam-Webster Online Dictionary
feedback (noun)1.
the return to the input of a part of the output of a machine, system, or process (as for producing changes in an electronic circuit that improve performance or in an automatic control device that provide self-corrective action)
2.
a) the partial reversion of the effects of a process to its source or to a preceding stage
b) the transmission of evaluative or corrective information about an action, event, or process to the original or controlling source , also the information so transmitted
3.
a rumbling, whining, or whistling sound resulting from an amplified or broadcast signal (as music or speech) that has been returned as input and retransmitted
