n.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.
c. Sound created when a transducer, such as a microphone or the pickup of an 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; 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.