ROM = Read Only Memory. Though a CD-R can be written to, generally, it's only once. Then the CD can only be read and being a form of memory, can be called ROM or CDROM when applied to a CD. All music...
The term "CD" means Compact Disk..so there really is no product just called a "CD"..it must be CD-ROM, CD-R, CD-RW,etc. "CD" means the same thing in all categories. The difference lies in the letters...