If you have similar content featured on several pages (two or more) on your website, you can use the rel=”canonical” tag to tell Google which page you want them to index and display in search results.The page you want displaying is called your canonical page. Note that Google will still crawl all of the pages, and will only use this one if they agree with your direction about it being the best and most relevant.
Telling Google you want a certain page as the canonical one is easy. All you do is all the following piece of code into the of the pages you don’t want to display:
This is most commonly done when a website has a www. and a non www. page, as well as a homepage with and without /index.html or .html at the end of the URL.