extension

A filename extension, file name extension or file extension is a suffix to the name of a computer file (e.g., .txt, .docx, .rs). The extension indicates a characteristic of the file contents or its intended use. A filename extension is typically delimited from the rest of the filename with a full stop (period), but in some systems it is separated with spaces. Other extension formats include dashes and/or underscores on early versions of GNU Linux and some versions of IBM AIX.Some file systems implement filename extensions as a feature of the file system itself and may limit the length and format of the extension, while others treat filename extensions as part of the filename without special distinction.

View More On Wikipedia.org