Information Architecture > 301 Redirect
A 301 redirect is a PERMANENT redirect, which can point old pages to new.
Used for your domain, any visitor going to www.yourdomain.com will be redirected to yourdomain.com, or vice-versa.
Search engines will "consolidate" your links with a 301 redirect, as otherwise it may be seen as TWO SEPERATE WEBSITES, you will no longer loose value of your links.