hi doorway pages are the pages which doesn't nay relation to the website content, used only as entrance gate of the website, so that user can enter, its a black hat technique.
Doorway pages are webpages that are specially designed to draw search engine visitors to your site.and it is black hat seo technique also known as bridges ,gateways or entry pages.
Doorway page Also called a gateway page. It's a black hate technique. A doorway page exists solely for the purpose of driving traffic to another page. They are usually designed and optimized to target one specific keyphrase. Doorway pages rarely are written for human visitors. They are written for search engines to achieve high rankings and hopefully drive traffic to the main site.
it is when pages and resources that are created especially for search engines’ robots; they contains many keywords
Doorway pages creation is a Black Hat Procedure. There are the pages that regular visitors can't see, but search engine spider can. They are used to tricks the search engines so that the sites gets a higher ranking. Not only they go against the rules but they also hurt the visitors experiences