To a portal page: This is a redirect from any page inside or outside of portal namespace to a page in that namespace. The above category link leads to a list of redirects from inside portal space. For a list of redirects from outside portal space, see Category:Redirects to portal namespace.
From a shortcut: This is a redirect from a shortcut in any namespace to a page in any namespace.
Shortcuts are wikilinked on community pages, talk pages, and edit summaries, but not in mainspace articles.