What are file extensions?

Different computer applications use different file types. The name of the file is followed by a period (sometimes referred to as "dot"') and the file extension.    Files are differentiated by a two to four letter file extension. These file extensions are used by computer applications to identify useable files. You can usually change a file's name, but it is best not to change the file extension.

Other than HTML, which file formats are most common on the Internet?

HTML files predominate.  Adobe's PDF (Portable Document Format) files are the second most common type of file found on the Web.  Microsoft Word documents, and PostScript files are also common.  Image, video, and audio files remain relatively rare when compared to other file formats on the Internet. 

Authored by Dennis O'Connor