Do you have duplicate pages on your website that have different URLs due to Search results, categories, SessionIDs, or some other quirky thing that your site does? Do you wish those duplicate pages would link to a preferred version of that page for SEO purposes? If so, Canonical URLs will help you accomplish just that.
A canonical URL allows you to set the version of the page that you want all duplicates to refer to for SEO purposes. When a person navigates to one of the duplicate pages, they will not be transferred to the preferred page, but anything related to traffic, link popularity, etc. of that duplicate link will be used for the canonical page.
Take the following example:
Let’s say you have the following web pages which all have the same content:
Now if you want the preferred or canonical page to be www.example.com/product123 you will add the following tag to the head section of the other two pages:
<link rel=”canonical” href=”http://www.example.com/product123″ />
Setting canonical links to the preferred version of the page will help with your site rankings and traffic because the major search engines will see the canonical link in the duplicate web pages and refer to the that link instead.
Check out this post for Google to get more information on canonical URLS. So take a look and add more ammunition to your SEO arsenal.