An ISO file, also called an ISO image, is a type of file containing an entire representation of a CD, DVD or Blu-ray disc. ISO files are commonly used to distribute operating systems on the Internet such as Windows 7 and Windows 8, as well as large program files.
A number of different applications exist that allow users to open, create and burn ISO files. The GNU/Linux and Mac OS X operating systems have the ability to "mount" ISO files directly, enabling users to explore the contents of the file without having to burn the image to a disc or install special software.
ISO files can also be burned to a USB flash drive, an option which can be helpful for a computer lacking a traditional optical drive.