u have a domain suppose
http://www.google.comyou have a site suppose www.geocities.com
you set a url forwarder at google.com which forward it to geocities.com
when person access google he will be taken to geocities but the person will be able to see geocities.com in address bar
if u do url cloacking
the person wont be able to see geocities.com in the address bar , he will still see google.com in address bar but he will be on geocities.com
hope this helps