ION is the extension of files used in various applications. Such files are used to store a description of the content of another file to which it has been assigned. Such information may be, for example, metadata, date of creation and last modification of the file, name, etc.

Depending on the program the ION file is used by, it can have a different format, but most often it is a plain text file. You can often see such a file as descript.ion and it is referred to as the description file.