1. The return of part of the output of a system to the input. Negative feedback causes self-adjustment of the system and therefore stability . Positive feedback causes instability. See closed loop system .
2. The information that a computer-controlled fuel system returns. The sensor measures the oxygen content of the engine's exhaust in order to keep the fuel-air ratio very close to the ideal proportion for combustion. Such tight control of the fuel-air ratio is required for the proper operation of three-way catalysts.