Google Canonicalization?

Q: What is a canonical url? Do you have to use such a weird word, anyway?

A: Sorry that it’s a strange word; that’s what Google calls it. Canonicalization is the process of picking the best url when there are several choices, and it usually refers to home pages.

For example, most people would consider these the same urls:
www.example.com
example.com/
www.example.com/index.html
example.com/home.asp

But technically all of these urls are different. A web server could return completely different content for all the urls above. When Google “canonicalizes” a url, we try to pick the url that seems like the best representative from that set.

For More info on the post:
http://www.mattcutts.com/blog/seo-advice-url-canonicalization/