(1) A simulated file folder in storage. "Directory" was first used in the Unix and DOS environments. Apple introduced "folder" for the same structure on the Mac, and Windows followed. See
folder.
(2) A database of users and devices in a network. See
network directory and
metadirectory.
(3) A database of websites organized by subject that is used by search engines. Yahoo! was a directory site in its early days, but then added search bots to automatically index pages as the Web grew too large to manually index. See
Open Directory Project,
Web search engines,
metasearch sites and
Yahoo!.