seo-first.swf
Canonicalization (Man it is hard to say that), is the practice of choosing one version of several duplicate pages and redirecting the other pages to the chosen one. In this video, Alex Centeno explains the process. This video is the first video of my SEO Basics collection, therefore it is horrible in terms of language and theme (I hope they get better with time). Anyhow for anybody looking for the .htaccess code for the www versus non-www canonicalization it is here:
RewriteEngine on
RewriteCond %{HTTP_HOST} ^yoursite.com [NC]
RewriteRule ^(.*)$ http://www.yoursite.com/$1 [L,R=301]