Doorway Pages

Pages designed to rank for highly targeted search queries, typically designed to redirect searchers to a page with other advertisements. Some webmasters cloak thousands of doorway pages on trusted domains, and rake in a boatload of cash until they are caught and de-listed. If the page would have a unique purpose outside of search then search engines are generally fine with it, but if the page only exists because search engines exist then search engines are more likely to frown on the behavior.