The ability of the Microsoft® Windows® installer to restore the target machine to its preinstallation state if the product installation is unsuccessful.
When the Windows installer processes an installer package (.msi) file for the installation of a product or application, it simultaneously generates "rollback" information and saves a copy of every file deleted during the installation. If the installation is unsuccessful, the installer automatically performs a rollback installation that returns the system to its original state. If the installation is successful, the installer deletes the file copies and rollback information that it saved.