A floppy disk is a magnetic data storage device that is composed of a circular piece of thin, flexible (i.e. "floppy") magnetic storage medium encased in a square or rectangular plastic wallet. Floppy disks are read and written by a floppy disk drive.
The image to the left is a 3.5" floppy, and will probably hold 1.4 megabytes of data. An older, floppier format is the 5.25" floppy. The 3.5" floppy disk format was introduced by Sony in 1982, with its Sony SMC-70 computer. 3.5" floppy disks would become the standard storage medium for personal computers up until the 1990's.
Floppy disks are being phased out in the PC industry - companies like Apple and Dell have removed floppy disk drives from newer models of their computer systems. The format has been all but replaced by compact discs, which in turn are being made obsolete by the DVD.