Reading view is a new feature in Internet Explorer 11 for Windows 8.1 that helps you focus on the main content of the Web page you want to read. Reading view is a way to experience just the article or blog post you want to read, without the distractions of related (or unrelated) content surrounding the story. Find an article you want to read, switch to reading view, and settle into a great reading experience. When you’re done, just exit reading view to continue browsing on the site.
Source : IEBlog