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 -
someone who takes the place of another (as when things get dangerous or difficult); "the star had a stand-in for dangerous scenes"; "we need extra employees for summer fill-ins"
voice,
part a means or agency by which something is expressed or communicated; "the voice of the law"; "the Times is not the voice of New York"; "conservatism has many voices"
descant,
discant a decorative musical accompaniment (often improvised) added above a basic melody
A backup or the process of backing up refers to making copies of data so that these additional copies may be used to restore the original after a data loss event. The verb is back up in two words, whereas the noun is backup (often used like an adjective in compound nouns). Backups are useful primarily for two purposes.