Redundancy is a system design in which a component is duplicated so if it fails there will be a backup. Redundancy has a negative connotation when the duplication is unnecessary or is simply the result of poor planning. 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. This allow a fail safe system when something goes wrong. Having an electricity generator for when the power goes out is an example of redundancy.
So what do you do in a situation with computers? how do you build redundancy? If you have a system in place and it fails, how long is it going to take to get a backup working? These are questions that are often discussed in company meetings when it comes to their computer system.
in computing, the term is used more specifically and refers to duplicate devices that are used for backup purposes.