a file that has an .iso extension indicates what type of file
ISO image An ISO image is a disk image of an optical disc. In other words, it is an archive file that contains everything that would be written to an optical disc, sector by sector, including the optical disc file system.[1] ISO image files bear the .iso filename extension. The name ISO is taken from the ISO 9660 file system used with CD-ROM media, but what is known as an ISO image might also contain a UDF (ISO/IEC 13346) file system (commonly used by DVDs and Blu-ray Discs).