A directory is, in general, an approach to organizing information, the most familiar example being a telephone directory.
1) On the World Wide Web, a directory is a subject guide, typically organized by major topics and subtopics. The best-known directory is the one at Yahoo (http://www.yahoo.com). Many other sites now use a Yahoo-like directory including major portal sites.
2) In computer file systems, a directory is a named group of related files that are separated by the naming convention from other groups of files.
3) In computer networks, a directory is a collection of users, user passwords, and, usually, information about what network resources they can access.