Learn in the textbookOptical Disc Storage Media — CD, DVD, Blu-ray
DefinitionA CD-ROM is a CD whose contents are recorded at manufacture; the user can only read it and can neither write to it nor erase it.
ExplanationThe contents are stamped from a master disc into pits on the recording surface, so identical discs can be mass-produced cheaply. That made it a long-standing choice for handing out unchanged content to many people, such as software and dictionary data. It is also non-volatile, keeping its data without power.
AnalogyLike a printed, bound book: you can read it, but you cannot add your own writing to its pages.
Memory hookROM stands for Read Only Memory, so the name says outright that it is memory you can only read.