Apple PowerBook (Duo 270C) - Manual (Page 59)

Different types of icons represent different types of containers.
Hard disks and floppy disks are like filing cabinets. You use disks
to store files—your programs and the documents you create
with them.
Shared disks are like filing cabinets containing office supplies or
information that you share with others in your work group. Your
PowerBook needs to be connected to a network before you can
use shared disks.
Folders are like folders in a file drawer. You use folders to
organize your files.
Programs are files containing instructions to the computer that
let you do certain types of work.
Chapter 2: Working on the Desktop 43