1. the property of having more structure than is minimally necessary. Biological systems or structures often have redundancy so that impairment or failure of a unit will not prevent adequate functioning of the whole. See also distributional redundancy.

2. in linguistics and information theory, the condition of those parts of a communication that could be deleted without loss of essential content. In this sense, redundancy includes not only obvious padding, such as repetitions, tautologies, and polite formulas, but also the multiple markings of a given meaning that are required by many conventions of grammar and syntax. For example, in the sentence All three men were running, the plurality of the subject is signaled four times: by all, three, and the plural forms men and were. It is largely owing to redundancies of this kind that one can so often guess the correct content of messages that have been only partially heard. Redundancy has been estimated to constitute roughly 50% of most written and spoken English. —redundant adj.