A filename or file name is a name used to uniquely identify a computer file in a directory structure. Different file systems impose different restrictions on filename lengths. A filename may (depending on the file system) include: * name – base name of the file * extension (format or extension) – indicates the content of the file (e.g. .txt, .exe, .html, .COM, .c~ etc.) The components required to identify a file by utilities and applications varies across operating systems, as does the syntax and format for a valid filename.