Text-based file used for describing the contents of another file or files; may specify the other files' filename, file extension, metainfo, and other information; often named descript.ion; used by file system managers and software programs for organizing and reading file information.

The descript.ion file (which reads "description" but with "ion" as the three-letter extension) has been used in various contexts, including with older bulletin board systems (BBSs), 4DOS (an alternative MS-DOS command-line interpreter), and with extensions to Drupal CMS software, such as Filebrowser and File Tree. XnView also supports ION files to export and import metadata in the program. NOTE: Since descript.ion files have been used in different contexts, the format may vary between the different software programs that use them.