noun feed·back \ˈfēd-ˌbak\

    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