|1. Backup is the practice of copying a file onto a disk or tape using a utility. This is done for protection in case the active disk file gets damaged. |
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2. A process by which data, electronic or paper-based, is copied in some form so as to be available and used if the original data from which it originated is lost, destroyed or corrupted.
(Source: Business Continuity Institute - BCI)
These additional copies are typically called, "backups." Backups are useful primarily for two purposes; (a) to restore a state following a disaster (called disaster recovery) (b) to restore small numbers of files after they have been accidentally deleted or corrupted. Backups are typically that last line of defense against data loss, and consequently the least granular and the least convenient to use.