In information theory, a designation for the existence of superfluous elements in a message, which do not supply additional information, but only support the intended basic information. In reactor technology, all safety-relevant measuring values, e.g. the neutron flux density in the reactor are determined by three measuring systems which are independent from one another and only the value indicated by at least two systems is considered correct. The multiple design of important technical systems (emergency cooling system, emergency power devices) is also called redundancy.

Schematic diagram of redundancy for the closing function
(a) and opening function
(b) of valves in a pipe