File Extension (File Format)

A file extension, also known as a file format, describes how the data within a file is organized. This indicates characteristics of the file’s contents or its intended use. It is identified by the extension name which follows the description of the content of the file in a 3 to 4 letter suffix with a period before. Applications examine the extension and determine whether or not they can access the data in that file. The most commonly known file extensions are Microsoft Word documents (.doc), web pages (.html), web page images (.gif and .jpg), Adobe Acrobat files (.pdf), and executable programs (.exe). File extensions are the most common way to imply information about the way data might be stored in the file.