"Doorway pages are typically large sets of poor-quality pages where each page is optimized for a specific keyword or phrase. In many cases, doorway pages are written to rank for a particular phrase and then funnel users to a single destination.

Whether deployed across many domains or established within one domain, doorway pages tend to frustrate users, and are in violation of our webmaster guidelines."

google.com/support/webmasters/ ...

I've archived the original at my blog:
beussery.com/blog/index.php/20 ...