Backup

Backup is 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 (thefreedictionary.com). A backup is a copy of one or more files created as an alternate in case the original data is lost or becomes unusable. For example, you may save several copies of a research paper on your hard drive as backup files incase you decide to use a previous revision. Better yet, you could save the backups to a USB flash disk, which would also protect the files if the hard drive failed. Files can be mistakenly deleted or corrupted by viruses or other software attacks. Program installation conflicts can make applications or files unusable. There are unfortunately many ways for your data to become damaged or disappear. That is why it is so important to backup your data. Most people don't realize the importance of having a backup until it is too late. Of course, when you have lost years of photos, school papers, business documents, e-mail archives, music, movies, or any other data that you cannot recover, the importance of having a backup becomes all too real. (businessdictionary.com)