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...
Compact Disk Read-Only-Memory. Read-only-memory refers to a long-term memory solution. You have it in your computer under the form of a hard drive. Files and programs are stored in Read-Only-Memory...