Doorway pages are specially optimized pages for one search engine and 1-3 keywords. They are also known as gateway, bridge, entry, jump and supplemental pages. Companies use doorway pages to achieve higher search engine rankings by giving each search engine what it wants.
Doorway pages stand on their own, separate from the rest of the site. These pages usually feature a logo, some text and a link that asks visitors to enter for more information.
Importance of doorway pages:
Doorway pages provide web masters with an opportunity to rank high for any keyword, with any search engine. If a site contains dynamic content, frames, multimedia files or large graphics, doorway pages are a must. Never use doorway pages for Directories, which use humans to review web sites, don't enjoy doorway pages. You risk being blacklisted by submitting a doorway page to a directory. Since people don't need to see your HTML, its optimization is unnecessary. Can help rank high for any keyword in any engine - optimize for one keyword, one engine
Don't create them for directories - Learn what search engines want - Don't spam