1 a : the transmission of evaluative or corrective information about an action, event, or process to the original or controlling source also : the information so transmitted b : the partial reversion (see reversion sense 3a) of the effects of a process to its source or to a preceding stage 2 : 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) 3 : a rumbling, whining, or whistling sound resulting from an amplified or broadcast signal (such as music or speech) that has been returned as input and retransmitte­d