Regular rendition is the process of simply returning a prisoner to their home country. Extraordinary rendition is where an enemy combatant is captured and sent straight to another state without setting foot on American soil. The CIA uses extraordinady rendition in order to bypass a US-signed anti-torture treaty. They export prisoners to countries where they know they will be tortured for information.
One senior level CIA man once said that if you want a good interogation, send them to Jordan, if you want them tortured, send them to Syria, and if you want them to just outright dissapear, send them to Egypt. (source: Wikipedia. Ha!)