An ISO image is a disk image of an optical disc (CD or DVD). 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.
The name ISO stands for International Organization for Standardization is an international standard-setting body composed of representatives from various national standards organizations. I only mention this because the initialism ISO is used for various things, most commonly photographic film sensitivity.
ISO disk image is used to preserve / share the contents of a CD or DVD without actually having the actual CD or DVD.
Burning A Disk
From a image you can do various things most often turning them back into CDs or DVDs. This can be accomplished in Windows by using any CD or DVD recording program like InfraRecorder and choosing the “Write Image” function. The terminology can change depending on the program.
One other things you can do with a ISO file is to make a bootable thumbdrive. This can’t be done with any image to flashdrive program because many programs will not create a media that can be booted from a UEFI (The modern more secure version of BIOS). I’m sure there are many programs that do this but I personally am only familiar with Rufus and UNetbootin.
You may have to change settings in your UEFI setup to get it to boot. This is specific to each PC manufacturer. Google it! On my Asus X551m I had to disable “Secure Boot Control” and change the boot order.
The third thing you can do with an ISO file is create a virtual machine. A virtual machine is a full operating system running within an other. Example: Linux inside of Windows, or Windows inside of Linux, etc. You do this with the help of a program like VMware (a commercial product) PC only, Virtualbox (free) on Windows Mac, Linux, and Parallels (a commercial product)on Mac only). You can usually do this with any computer but on slow computers with little memory like mine will run very slow and may not work at all.
Installing a virtual machine after selecting the appropriate environment is just like installing the OS from a disk or USB device but the boot device you will select will be the ISO file itself.