Also see flat file , an entirely different term.
A flat file system is a system of files in which every file in the system must have a different name. In Windows 95 and most other operating system today, files are managed in a hierarchical file system with a hierarchy of directories and subdirectories, each containing a number of files (or subdirectories). The operating system allows more than one file to have the same name as long as it is stored in a different directory. Early versions of the Macintosh and DOS operating systems used a flat file system.
The term flat file directory is used to describe a file directory that can contain only files (no subdirectories).