An ISO image (also referred to as an ISO file) is a type of disk image that is comprised of all sector data in an optical disk, including its file system. Optical disks include such media as CDs, DVDs and Blu-ray disks.
Many programs can process ISO files directly. You can create ISO images from optical disks and save their contents, or just the file system, to a file. A common use for an ISO image is for temporary storage before writing to a blank CD-R or DVD-R to produce an identical copy of the original disk.