A backup or assistant pilot of an aircraft.
To serve as relief or assistant pilot.
A machine or person that folds things.
An organizer that papers are kept in, usually with an index tab, to be stored as a single unit in a filing cabinet.
A folding knife, typically a pocketknife.
A virtual container in a computer's file system, in which files and other folders may be stored. The files and subfolders in a folder are usually related.