What is a disc envelope?(What is, Concept and Definition)

Sometimes called disk cover or disk sleeve , the disk envelope is a paper or plastic sleeve that is a disk 5.25-inch and his jacket is stowed.They were used because the 5.25 "floppy disks had unprotected areas that allowed the computer to read from the floppy, but when they were not on the computer they were vulnerable to dust, dirt, and hair.