What is RedirectPermanent in ASP.Net?
A redirect will send an 302 HTTP response while a RedirectPermanent will send a 301 response. See https://en.wikipedia.org/wiki/List_of_HTTP_status_codes for a complete overview of response codes.
The difference between both is small but the permanent redirect will change the URL that was used in the browser. With a normal response you would be redirected but the browser could choose to display the old URL.