The terms Recovery disc (or Disk), Rescue Disk/Disc and Emergency Disk all refer to a capability to boot from an external device, possibly a thumb drive, that includes a self-running operating system: the ability to be a boot disk/Disc that runs independent of an internal hard drive that may be failing, or for some other reason is not the operating system to be run.

The focus of recovery or rescue is not to lose the data files on the hard drive; the focus of restore is to restore the operating system's functionality (and subsequently restore the contents of one's latest backups).

The rescue/recovery tool uses media containing a backup of the original factory condition or a favored condition of a computer as configured by an original equipment manufacturer or an end-user. OEM supplied media are often restore tools shipped with computers to allow the user to reformat the hard drive and reinstall the operating system and pre-installed software as it was when it was shipped. Many modern systems have eliminated use of a physical recovery disc and instead store this software in a separate partition on the hard disk itself.