You might be asking what is the term “canonical”? What canonical means is that a given item is the authority, or preferred reference for other items. In terms of Google’s new element, what it allows you to do is to allow you to be able to point disparate objects (PDF’s, content on CDN’s, etc.) to a page on your site, so that it will be pushed up further in search results.
For example, if you are running an e-commerce site and you have a list of products, but those products can be sorted by various means such as price, availability, name and so forth. Your pages maybe setup like this:
http://www.yoursite.com/products.html?product=fishing_tackle&sortby=name
http://www.yoursite.com/products.html?product=fishing_tackle&sortby=price
In order to implement canonicalization you add the following code in the <head> section of your HTML files above:
<link rel=”canonical” href=”http://www.yoursite.com/products.html?product=fishing_tackle”/>
For a complete reference how this element works please visit: http://www.google.com/support/webmasters/bin/answer.py?answer=139394
