positive feedback

Short definition from Wiktionary

Noun

1. 1
   A situation where some function of the output of a system, process, or mechanism is fed back in a manner that tends to increase any divergence of the output from its initial value: A feedback loop in which the output of a system is amplified with a net positive gain and added to the input signal before the main amplifier.
2. 2
   A situation where some function of the output of a system, process, or mechanism is fed back in a manner that tends to increase any divergence of the output from its initial value: Feedback which builds upon previous feedback.