In order to transfer information from one computer to another, data can be stored on a "floppy disk", a

secondary storage device, in the form of a flat, circular flexible disk on to which data can be stored in a magnetic form (a floppy disk cannot store as much data as a hard disk, but is easily removed, and is protected by a flexible paper or plastic sleeve); the current standards are three and a half-inch diameter disks which can store 720Kb or 1.44Mb of data or five and a quarter-inch disks which can store 360Kb or 1.2Mb. PCs and Macintosh computers normally use the three and a half-inch 1.44Mb standard (but with different formatting).

(S.M.H. Collin [ed.], Dictionary of Multimedia, Peter Collin Publishing, Teddington, Middlesex, 1995, p105)

Floppy disks are "played" in the computer's "floppy disk drive", inserted through a slot in the Central Processing Unit or CPU (the "box" part of the computer).

The Amstrad PCW which I used for my MA was unusual in that it used two and a half inch wide disks; there was no hard disk drive and all work was stored on floppies.