You must have come across Joomla components where the Meta Description are not available and you can't see to override it from the Menu item Meta Tag option. I too came across such thing, so thought how to achieve this. My client was asking me to change the Description as it was displaying a wrong description in Google Search... Thought how i could achieve this thing. Finally came up with this brilliant idea.
Open up your FTP or cPanel File Manager and then navigate to your template folder and then html. In short we are going to use template overrides feature of Joomla. I will not be going into detail what template overrides is. In the default.php file of your template overrides located at yourtemplate/html/com_your_component_name, just after the code defined( '_JEXEC' ) or die( 'Restricted access' );: add the following
$document =& JFactory::getDocument();
$document->setDescription("Your custom description");
I will here demonstrate for a component called JSPLocation, which is a Location Displaying Component. When you use this Component, it will not include a Meta Description in the source code. lets copy the contents of the folder components/com_jsplocation/views into your local drive.
You will have something like
Now create a new folder called com_jsplocation inside yourtemplate/html and then another folder called jsplocation. Inside this folder upload the contents of components/com_jsplocation/views/jsplocation/tmpl which you just downloaded in the above steps.
You will have 3 files called default.php, default.xml and index.html.
Open up default.php in a text editor and then edit it, check the image below
That's it now check your Source code...
Please note that this hack is only for Joomla 2.5+ and higher versions only.