Similar and Duplicate Pages
Duplicate pages can have a very negative effect on SEO ranking. However, it is almost impossible not to have some duplicate pages on a site dedicated to a single topic. Session IDs, print friendly versions, and URL parameters all can create duplicate pages. There a few ways to deal with this.
First, you can set up a 301 redirect that allows all identical pages to merely redirect to a single URL. Second, and less labor intensively, you can use a canonical tag, or rel=canonical. This tells search engines which page of several duplicates is the important or main one. You can add this tag to the HTML head of the page. It’s a fast and easy way to tell crawlers how to analyze duplicate content.