The situation in which outputs feed into the inputs, either directly (positive feedback), creating either too much output or a corrupted output, or in opposition (negative feedback), which can be used to regulate and stabilize a system.

In an audio world, this is the lovely noise that is created when you point your microphone at the speakers, called Larsen effect.

This is also observed in closed groups, where an idea is fed into the group and circulates to the point where alternate ideas are ignored. This is the cause of a lot of 'expert discussions' (screaming matches) on the internet, where individuals from self-supporting groups clash.

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Also a means of controlling output where measurements of changes in output are compared to changes in input to the controlling elements.

''That is confusing. There are two types of feedback - positive and negative. It's easy to imagine roughly how both work, but a precise analysis is a bit awkward, due to the essential time delay.''