A three-letter (in most cases) code at the end of a filename that indicates what type of file it is.
This is the part of a file name which follows the last period. For example, in the filename index.html, the extension is .html. In the case of index.html.bak, the extension is .bak.
A three letter extension after a file name tell you what type of file it its. For example, WORD.DOC is a Word file whose file name extensions is .DOC.
The middle portion (between SEPARATOR 1 (.) and SEPARATOR 2 (;)) of the name of an ISO-9660 File within a Directory.
A set of characters added to the end of a file name that identifies the file type or format. See Also: file format , file type
The end of a file name in some operating systems where the name of a file ends with a period followed by (usually) two to four letters. The extension is used to associate an application program with the file. For example, the file containing this glossary is named glossary.doc. The file name extension is .doc. Clicking on the name of the file automatically opens the file with the Microsoft Word word-processing software.