There are several variations of bridge pages. A bridge page can be a separate, secondary home page customized for visitors who click on a specific banner or advertising link.
 
Bridge pages can also be pages that have been optimized for the search engines for particular keywords and keyword phrases.
 
Bridge pages are also referred to as entry pages, jump pages, doorway pages, gateway pages and portal pages. The gap between the entry and the destination page is where the name comes from.
 
Bridge pages are not a new concept. Many spammers have used them successfully for years to capture traffic. As a result, most search engines frown on doorway pages because of the potential for abuse. The best and most “clean” way to design bridge pages is to create a second website (with a different domain) as a text-only version for your main pages. Then insert a link on your text site to your main website. This will "bridge" visitors over to your main site.
 
It’s important to note that search engines generally no longer index pages using fast “meta refresh” (a special tag in the section of a document that tells the web browser to automatically redirect to a different page).
 
This was enforced in an effort to discourage abuses with doorway pages. To get around this some webmasters will do a code swap, which is submitting a text only page for search engine indexing then swapping it on the server with the "human" page once a ranking position has been achieved.
 
Code swapping is also called "bait-and-switch." The downside of this practice is that a search engine may revisit at any time and if it indexes the "human" page, the position could drop. Or worse, you could get dropped from the SE index altogether.