Definition of disk

A reusable magnetic storage medium. The floppy disk used today is the rigid 3.5-inch microfloppy that holds 1.44 MB. It is called floppy because the first varieties were housed in bendable jackets.

Generic term for a type of storage device, such as a- hard disk- or a- floppy disk- (diskette). So called because the important part, where the information is actually stored, is circular, although you can’t see it because it is hidden away inside a protective shell.