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1540s, "guide, book of rules," from Medieval Latin directorium, noun use of neuter of Latin directorius, from directus (see direct (v.)). Meaning "alphabetical listing of inhabitants of a region" is from 1732; listing of telephone numbers is from 1908. As an adjective, from mid-15c.
A node in a hierarchical file system which contains zero or more other nodes - generally, files or other directories.
The term "folder" is sometimes used in systems such as the Macintosh or Microsoft Windows in which directories are traditionally depicted as folders (like small briefcases).