ISO File
From ctowiki
An ISO file is an image (digital copy) of a CD or DVD in one large file. This file allows a program to properly recreate the structure of the CD/DVD. Many pieces of software from MSDNAA are distributed as ISO files.
If you want to make a CD/DVD with the ISO you have downloaded, you can use a program such as Nero to burn the CD/DVD. If you do not have a burning program that can handle ISO files, you can download the free program IMGBurn. Another option is to use a program such as Daemon Tools to add a virtual CD/DVD drive to your computer and mount the image. For more information on this, please read our tutorial Installing and Using Daemon Tools.
Related Tutorials
Installing and Using Daemon Tools
Burning a CD with Nero (old guide from Dept. of Foreign Language)