This article is about the computing term. The Directory was also a government in revolutionary France from 1795 to 1799.
In computing, a directory, catalog, or folder, is an entity in a file system which contains a group of files and other directories. A typical file system contains thousands of files, and directories help organize them by keeping related files together. A directory contained inside another directory is called a subdirectory of that directory. Together, the directories form a hierarchy, or tree structure.
If you imagine the computer's file system as a file cabinet, high-level directories may be represented by the drawers, while lower-level subdirectories may be represented as file folders within the drawers.
Historically, and even on some modern embedded devices, the filesystems either have no support for directories at all or only have a flat directory structure, meaning subdirectories are not allowed; there is only a group of top-level directories each containing files. The first popular fully general hierarchical filesystem was that of UNIX. This type of filesystem was an early research interest of Dennis Ritchie.
Strictly speaking, there is a difference between a directory which is a filing system concept, and the WIMP metaphor that is used to represent it (a folder).
Note that the folder metaphor may be misleading with regard to things like file permissions on UNIX: To rename or delete a file you need write permission to the directory that contains the file. This is perfectly understandable if the directory is seen as a list of filenames but not if it is seen as a container (as folder implies).
In graphical user interface (GUI) or WIMP environments, folders are often depicted with icons which resemble physical file folders such as those of a file cabinet in an office.
The word directory\ is also used in computing and telephony with a different sense: a central repository of information related to management of a computer or a network of computers. This includes data on users, applications, hosts, network devices, security credentials and more. The directory, as opposed to a database, is heavily optimized for reading, with the assumption that data updates are very rare compared to data reads.
The Distributed Management Task Force (DMTF) is creating standards related to the information stored in such directories, and the protocols and APIs used to access it. The main product of these efforts is a common information model (CIM) for management.