A bootable ISO (International Organization for Standardization) image is a type of image file that contains a bootable operating system, which can be used to start a computer in case of an emergency. It is a self-contained file that includes all the necessary files and drivers to boot a computer and run a specific operating system or utility. In the context of Acronis Cyber Protect Home Office, a bootable ISO image is created to provide a rescue environment that allows users to restore their system in case of a disaster.