re·dun·dan·cy

/rıˈdʌndənsi/ noun, pl -cies

1 a [noncount] : the act of using a word, phrase, etc., that repeats something else and is therefore unnecessary

Avoid redundancy in your writing.

1 b [count] : a word, phrase, etc., that repeats something else and is therefore unnecessary : a redundant word, phrase, etc.

Try to avoid using redundancies in your writing.

2 technical : a part in a machine, system, etc., that has the same function as another part and that exists so that the entire machine, system, etc., will not fail if the main part fails

[count]

The design incorporates several redundancies.

[noncount]

a system with a high level of redundancy

3 Brit

3 a : the act of ending the employment of a worker or group of workers

[count]

compulsory/voluntary redundancies [=layoffs]

[noncount]

The restructuring is expected to result in the redundancy of several hundred workers.

3 b [noncount] : the fact of being dismissed from a job because you are no longer needed

The workers are now facing redundancy.