What is X-Ray? (Amazon)

Amazon’s X-Ray uses the power of the net, and crowdsources (usually from Wikipedia or you can write your own custom descriptions) the answers to terms and difficult points in your book.  X-Ray can be found in the KDP dashboard, and is in the menu to publish your books (usually in the dropdown beside your book title which has Kindle ebook actions above the button.  If your book is in pre-order or published, it will appear above ‘unpublish book’.  
X-Ray is optional, but can be a great marketing tool, and is also great for books with lots of terms, like fatansy and sci fi or non-fiction books.