Mark has posted a very detailed post containing this Canonical URLs, a new feature in WordPress 2.3 and personally I like this feature a lot because some of my users are complaining to me that when they are using my WP-PageNavi, when they access http://example.com/page/1/ they do not get redirected to http://example.com, but I told them it is a WordPress issue over here and finally, this “bug” is gone for good.
So, what’s the problem with this? The URLs are all showing the exact same content, so why should it matter? Well, search engines can’t assume that all of these alternative URLs represent the same resource. So they don’t automatically get condensed into a single resource. As a result, you can actually end up competing against yourself in search engine rankings. So to avoid confuse search engines and to consolidate your rankings for your content, there should only be one URL for a resource. We call this URL the canonical URL. Canonical means “standard” or “authoritative”. It’s the one that WordPress generates, and it’s the one that you want everyone to use.