Wow, now I feel old. The original disks were literally floppy (as in flexible or bendable - though not recommended to bend them), and either 5¼ inch or 3½ inch. In both cases the data was stored on a flexible disc, though the 3½" disc had a hard case.

A floppy disk is a data storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles. They are read and written by a floppy disk drive (FDD). Invented by IBM, floppy disks in 3.5-inch (89 mm), 5.25-inch (133 mm) and 8-inch (200 mm) forms were an ubiquitous form of data storage and exchange from the mid-1970s to the 2000s

Thank you for the answers. Now I understand why it is called "floppy" disc.

Floopy Disc is one kind of storage type. They were used as a file or data storage just like USB FlashDisc that we use now days. フロッピディスクってデータ或いはファイルを保存するためのストレジの一種類です。 最近はこういうストレジはもうあまり使われていない。最近はCDやDVDやUSBフラッシュディスクが変わりに使われています。

フッロピーディスク    floppy disk In the old days when computers were new, you could insert a magnetic disc. It was 14cm in diameter, and it was very soft. Hence the name floppy disc. Some of them are just 9cm. Nobody uses them any more. http://images.google.com/search?hl=en&lr=&sa=N&tab=wi&q=%E3%83%95%E3%83%AD%E3%83%83%E3%83%94%E3%83%BC%E3%83%BB%E3%83%87%E3%82%A3%E3%82%B9%E3%82%AF&biw=1024&bih=506&tbm=isch