1. The fraction of the information in a transmission system that may be eliminated without loss of essential information. The excess information is often deliberately included to allow for loss in the transmission system.
2. The extra components, devices, or circuits included in an electronic circuit or apparatus to increase the reliability of the system. If therefore a fault develops in one portion of the system the redundant circuits or components provided can take over the function of the faulty part. Redundancy is very important in systems, such as aircraft systems, in which high reliability is essential.