A DVD-ROM is a computer disc of the DVD kind that holds much more than a CD-ROM. ROM here is read-only memory: the machine can read what is already on the disc, but you do not normally save new files onto it the way you would with a USB stick or a hard drive. Software used to arrive this way, in a box, for you to install. A movie DVD that you play on a living-room player is also a DVD, but people usually just say DVD; DVD-ROM is the computer, data-disc name. The letters DVD were sold both as digital versatile disc and, earlier, digital video disc — both names have been used. The whole thing is a little dated now. Many computers no longer have a disc drive at all, and a lot of programs arrive as downloads. You still meet DVD-ROM in older manuals, school labs, and “this PC has no DVD-ROM drive.”