A disk made of flexible plastic, as compared to a hard disk, which is made of metal. The term floppy is now usually applied only to disks with thin, flexible disk jackets, such as 5.25-inch disks. With 3.5-inch disks, the disk itself is flexible, but the jacket is made of hard plastic; thus, 3.5-inch disks aren’t particularly “floppy.” See 5.25-inch disk, 3.5-inch disk.