What file is this ??

What file is this ?? -- Linux general technology-Linux technology and application information. For details, refer to the following section. There is such a file mmm $ in my root directory.
File mmm $: iso 9600 cdrom filesystem data 'rhel/5.4 i386 dvd 'boottable)

Ls-l mmm $: 1573900288 byte full 1.5 GB


What file is it ?? After opening with vim, only the mmm $ string is available and cannot be edited. You can only shut down the mmm $ string.

It seems that I have copied something from the attached CD.
What is the symbol next?