A stock market, equity market or share market is the aggregation of buyers and sellers (a loose network of economic transactions, not a physical facility or discrete entity) of stocks (also called shares), which represent ownership claims on businesses; these may include securities listed on a public stock exchange as well as those only traded ...
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.
computer backup - (computer science) a copy of a file or directory on a separate storage device; he made a backup in case the original was accidentally damaged or erased. backup. duplication, duplicate - a copy that corresponds to an original exactly; he made a duplicate for the files.