an alphabetical list of words relating to a specific subject, text, or dialect.
Doorway pages are web pages that are created for spam-indexing. This means spamming the index of a search engine by inserting results for particular phrases with the purpose of sending visitors to a different page. Spammers use this technique to rank highly for specific search queries. They are bad for users because they can lead to multiple similar pages in user search results.
In 2015 Google announced "ranking adjustment" for sites utilizing doorway campaigns. Search consoles may send webmasters "Gateway Page" warning if any of these exist: empty pages, hard to find pages, illegitimate content (review, testimonial, gallery) i.e. customer- or staff-generated content or duplicate content across multiple sites.