A file extension is the last part of a filename, after the dot (e.g. ".pdf"). Most file extensions are three characters long, but they can be shorter or longer as well. File extensions are used to define the file type of each file. The operating system uses this information to select which application will open the file and choose the appropriate icon for the file.

Visit the Sharpened File Extensions Reference to view an extensive list of file extensions and their associated file types.

Updated: April 26, 2010