“Dual ranking” is a phenomenon that appears on Google’s search results pages when the same domain ranks for a search term twice in a row. Here’s an example for the search term “books.”
You can see that results for barnesandnoble.com appear one right after the other. But, they don’t rank so closely together by chance. Google purposely groups together domains that appear on the same search results page. Achieving this dual ranking for your web pages has many advantages: your domain earns more real estate on the SERP, users view you as more authoritative, and you can get a page to jump several positions forward in search results.
If one of your domain’s pages ranks #4 in a search for “widgets” and another page ranks #12, you can get that second page all the way to position #5 with only a little work. Remember: Google sets up dual ranking results when domains appear on the same page. If you optimize the second page to move from position #12 to #10 — and hence, appear on the first SERP with the other page — it will jump to position #5 to create a dual ranking with the other page.
To help optimize your lower ranking pages and get them to become dual rankings, try looking at the structure of the higher-ranking page. Take note of keyword placement in the metadata and copy and try to adapt that style to the lower-ranking page. Increasing the amount of internal and outside links that point to the lower-ranking page can also help.
In some cases, getting a page to move from the second SERP to the first SERP can be much easier than getting a page to move from position #5 to #1. But thanks to dual ranking, the benefits can be nearly as good.