What does Hallway Page mean?
This is a web page often created by webmasters who believe that it helps search engines find pages on a website that they might otherwise miss.
As such a hallway page (sometimes called a gateway page) is often no more than a set of links for spiders and robots to follow.
There is some dispute as to whether or not they work as submitting a comprehensive sitemap.xml file to Google and the other major search engines should ensure they are aware of all your pages anyway.
Hallway pages are also sometimes used for Black Hat SEO
where a webmaster is trying to fool search engines into thinking certain pages are more important than they are.
Take a traditional hierarchy example:
Home page > Product Lists > Televisions > LCDs
In other words it takes a user 3 clicks to get to the page about LCD televisions. Now some search engine algorithms say that the more clicks a particular page is from the home page, the less important it is. To counter this you could add a structure:
Home page > Hallway Page > LCDs
This is primarily to try and persuade search engines that the LCD page is more important than it is - but as this is dishonest it is Black Hat.