One who, or that which, folds; esp., a flat, knifelike instrument used for folding paper.
interface: A place to hold documents, applications, aliases and other folders on a Mac disk. Folders have icons on the desktop and hold virtually unlimited number of files. You move items into a folder by dragging the item's icon onto the folder. The easiest way to open a folder is by double-clicking on its icon. To put a file back into its folder, select it and choose Put Away from the File menu.
A sub-directory in DOS and Windows terms.