Google, Yahoo, and Microsoft announced support for a new link element designed to help clean up duplicate links on your site. This new element helps the search engine find the primary or canonical location of your page. This is a particularly handy tool if you have a number of dynamic pages that show the same information for one reason or another. This is something I have been waiting for quite some time. I have run into a need for an element like this when working with larger ecommerce websites and even my own WordPress. The search engines have done some automatic filtering but it isn’t necessarily accurate. Now as web developers, we can have them select the proper primary page for the SERPs. Obviously, this isn’t useful on every site but there will be times it will be quite handy.

It works by adding a simple tag to the HEAD section of your HTML

<link rel=”canonical” value=”http://www.stemkoski.com/page.php”/>

Would help clean up a set of URLs like

http://www.stemkoski.com/page.php?sort=desc

http://www.stemkoski.com/page.php?sort=asc

Making the search engine list page.php instead of page.php?sort=desc or sort=asc. Obviously choosing page.php as the primary isn’t always the goal. You very well may want both dynamic pages indexed. However, if they have duplicate content to page.php and some small customization, perhaps ranking, then you can select page.php as the default to be indexed.

If you don’t get it or want more info watch Matt Cutts from Goole explain it:
http://videos.webpronews.com/2009/02/13/breaking-news-matt-cutts-explains-canonical-tag-from-google-yahoo-microsoft/