The Official Google Webmaster Central Blog recently announced that they now support the ability for you to specify the preferred version of a URL. This means that following these guidelines will help you eradicate your site’s duplicate contents that Googlebot sees.
Why would you do such a thing? Simply because many black-hat SEO folks abuse duplicate content to gain search ranking and Google tries really hard to detect and penalize them. The last thing you want to do is present yourself as an SEO spammer to Google.
In the post, Google is saying that you can easily tell the Googlebot the preferred version of a page by specifying the following tag within your <head></head> tag:
<link rel="canonical" src="http://example.com/your/preferred/version/of/this/page"/>
Read on…