Make a backup before overwriting a file. The backup is removed after the file was successfully written, unless the 'backup' option is also on. WARNING: Switching this option off means that when Vim fails to write your buffer correctly and then, for whatever reason, Vim exits, you lose both the original file and what you were writing. Only reset this option if your file system is almost full and it makes the write fail (and make sure not to exit Vim until the write was successful). See backup-table for another explanation. When the 'backupskip' pattern matches, a backup is not made anyway. Depending on 'backupcopy' the backup is a new file or the original file renamed (and a new file is written). NOTE: This option is set to the default value when 'compatible' is set.

(default on with +writebackup feature, off otherwise)