The term PART OF CD-ROM can be broken down into three parts: ONLY (4 letters), READ (4 letters), and DISC (4 letters). The term ONLY refers to the fact that a CD-ROM is a type of optical DISC that can ONLY be READ by a computer. The term READ refers to the fact that a CD-ROM can be READ by a computer, allowing it to access the data stored on the DISC. Finally, the term DISC refers to the physical DISC itself, which is made up of a polycarbonate plastic substrate with a reflective layer.