Hi. It is a program that copies a CD to your Hard Drive as a CD Image. It can then load the virtual CD into a virtual drive and run the program from the image. This drive (or more than one drive) shows up like your other drives in My Computer.
The advantage is in running programs that need the CD without having to find them and load them physically. You just create a short cut that loads the CD in the drive and runs the program. I use it a lot and love it. I think there is a version that does DVDs now. You do need plenty of disc space.