Doorway page is also called entrance page, or information. Generally what it means is a web page that specifically designed contains more relavent keywords in a single page in order to rank higher in the spider search engines.
Common web pages usually are very board targeted and not themed around particular keywords or phrases because your average web pages are unfocused and not optimized properly.
A doorway page is a web page specifically designed to rank high in the Search Engines for a specific keyword or keyword phrase. Its NOT just a blank page with a link that redirects to your main page, but a powerful, content rich page packed with your keywords.
If you have web pages with specific subject areas, products, services or even localities then specific doorway pages can be created for each one, concentrating on the keyword content and meta tags specific to those pages. In this way, a travel site, for example, could create doorway pages for each of its destinations. A page specifically dedicated to search engine content for Los Angles, for example, will have a better chance in the search engine rankings than a page which tries to cover all bases - and be readable!
Search Engines generally give priority to URLs that contain keywords. It is therefore worthwhile considering the registration of keyword-rich domain names for your doorway pages. Using the above example, a doorway page for Los Angles could have the name www.los-angles-travel-tourism-tourist.com, remembering that these URLs are for Search Engines only and that customer information is still only found on your central site. Customers can enter at these doorway domain pages from Search Engines and then click-on to the central domain. Once the customer has arrived from the search engine the doorway page/URL has done its job.
Once you have selected your keywords and phrases (about 50 would be the normal) you need to build a doorway page for each keyword and ideally, for each major search engine. All the major engines look for different keyword density in the text, title and description so you need to do some research by doing a search using your chosen phrase or keyword and studying the top 10 results at each engine (if you can spot them, study high ranking doorway pages).
When you're ready to submit your pages to the Search Engines, submit only one page each day. If you've created several pages you'd like to submit, you may want to create an additional page that contains links to each of your doorway pages. That way, you can submit just your link page and let the Search Engines crawl the rest of your links.
Creating doorway pages is a powerful way to increase your website traffic, but don't stop at just one. Imagine how much traffic you'd receive with 100 keyword packed doorway pages all pointing to your website.