In acoustics, the undesirable leakage of audio from loudspeakers, back into the same microphone which is being used for originally capturing the audio. If too much feedback occurs, the system can go into self-oscillation, causing unpleasant howling or squealing. In electronics, such as power amplifiers, feedback can be used to achieve specific results, such as performing input/output comparisons.

a condition where the output of a circuit recycles through its input. Acoustic feedback is a whine or howl that occurs in live audio situations when an amplified sound re-enters a sound system through the same microphone (or guitar pickup) that reproduced the original source, creating a loop. Feedback also can be used in signal processing; for example, part of a signal routed through a digital delay can be fed back into the delay to create a more complex effect.