Device type "loop" in mount command

Solution 1:

A "loop" device in Linux is an abstraction that lets you treat a file like a block device. It's specifically meant for a use like your example, where you can mount a file containing a CD image and interact with the filesystem in it as if it were burned to a CD and placed in your drive.

You can find more information on Wikipedia.

Solution 2:

The loop option to mount (it's not a type, it's an option) tells mount that this is a "loopback" device - a regular file to be used as a block device.

In the background, mount sets up a loopback device (/dev/loopX), then mounts that at /media/cdrom0.