Filename Extension

A filename extension is the part of the name following the last occurence of a dot. The purpose of the extension is to identify the type of the file.

For instance, the filename “index.html” has the extension “html”.

File extensions are often hidden in the Finder, but are nonetheless present as part of the filename. You can check the extension of a file following these steps:

To check the real name of a file, which includes the file extensnion:

  1. Select the the file in the Finder.

  2. Choose Get Info from the File menu.

  3. Disclose the Name and Extension triangle.

The part of the filename following the last dot is the extension.

Note: a file may have no extension.