Feedback is when a device, usually a microphone or a guitar, picks up its own signal being put through speakers. It then feeds it back into the amp, and out the same speakers, picking it up again, amplifying it thousands of times instantly.

How do you make it? Stick a microphone in front of a speaker and crank the volume. Stick a guitar in front of a tube amp and crank the volume.
its when a sound recieving device (microphone, etc.) picks up the sound coming out of the speaker it is plugged into, and amplifies and retransmits the sound, starting a loop. Something like that.

On guitar, i think it may have more to do with harmonics and sympathetic vibration, but regardless of the physics, it is achieved by turning the distortion up and bringing the guitar close to the amp
Mr.Pillow, i have to disagree on one thing. Solid state amps work as well. They just suck.
Listen to punk.
The scretching sound coming through the amps and speakers is the feedback.
If you know how to deal with it, feedback rocks!
If you can't tame it, it'll sound horrible...!

Its the sound from the guitar/mic looping through the speakers and back into the mic, back into the speakers. It causes a constructive waveform causing a high pitched amplifying tone.

This should help:
Last edited by af_the_fragile at Mar 24, 2008,