AVATAVA

Take a look at the link rel canonical tag and how to use it

The element: link rel="canonical" E.G. <link rel="canonical" href="http://www.webgears.com/index.html"> is designed to give search engines the preferred version of your URL. Simply add the element between the head tags of your page.

You should care about using this element in your pages to avoid duplicate content issues. When you have multiple URLs which can resolve to the same content, the search engine itself must decide which URL is correct-- and while the choice they make is usually correct, why take a chance? Another reason to care about using this element is that duplicate content appearing under a large number of URLs can make your site appear to be spammy to the search engines.

An important difference between using rel=canonical and 301 redirects is the rel=canonical can only be used within the same domain. A good use for this tag is to be certain the search engine uses the HTTP version of your site versus the HTTPS version. The HTTPS would be much slower and obviously a duplicate of the HTTP version of your public pages, right?

For an in-depth discussion, Google's Matt Cutts discusses the link=rel "tag", or rather "element" in the video below.