A diskette is a floppy disk: a small, flat square that old computers used to store files. You pushed it into a slot on the machine. It did not hold much — a school paper, a few pictures, a simple game. The later kind, about the size of a palm, had a hard plastic shell; the older kind was truly soft and floppy, which is where the other name comes from. Though actually, diskette and floppy disk are the same object, not two different gadgets. Diskette is a slightly more technical or catalogue-ish name, built to sound like cassette. Almost nobody uses them now. USB sticks and the internet replaced them. You will still see a little picture of a diskette as the Save icon in some programs, which tells you how old that picture is. Younger people may never have held one. If you meet the word, it is usually in a story about the 1980s and 1990s, or on a box in a drawer.