1. (a). The return of a portion of the output of a process or system to the input,especially when used to maintain performance or to control a system or process.

(b). The portion of the output so returned.

©. Sound created when a transducer such as a microphone or electric guitar picks up sound from a speaker connected to an amplifier and regenerates it back through the amplifier.

2. The return of information about the result of a process or activity; an evaluative response: asked the students for feedback on the new curriculum.

3. The process by which a system, often biological or ecological, is modulated, controlled, or changed by the product, output, or response it produces.