What triggers this issue?
This issue reports the URLs of the website that have no incoming internal links. These pages were either specified as seeds for the crawl or were found in the sitemap file.
Why is it important?
Website visitors won't be able to navigate to the orphan page from your website.
How to fix it?
Check your website navigation and link architecture to make sure that all relevant pages are easily accessible. Note that the pages you want to be indexed (and ranked) in the search engines should have a good number of relevant "followed" internal links.