There are two types of audio feedback: acoustic and electronic.
(1) Acoustic feedback is where a gain control is set too high in a sound reinforcement system and the amplified sound enters the microphone and is reamplified until a steady howl or whistle is heard. This is also called regeneration.
(2) Electronic feedback (or negative feedback) involves the application of a small portion of the output voltage of an amplifier to the input so as to cancel part of the input signal, reducing the gain of the amplifier, but also reducing the distortion and noise introduced by the amplifier.
(3) A specific application of feedback in FM synthesis, where at least one operator in each algorithm is equipped with a feedback loop.