[This documentation is preliminary and is subject to change.]
Metro style apps are the focal point of the user experience on Windows 8 Consumer Preview, and great Metro style apps share an important set of traits that provide a consistent, elegant, and compelling user experience.
At this point, you might be asking, "OK, so what are Metro style apps and how do they differ from desktop apps?" Metro style apps are immersive and chromeless, filling the entire screen so there are no distractions. Metro style apps work together, making it easy to search, share, and send content between them. When users are connected to the internet, their apps show them the latest content so that they can stay up to date. With a connected account, users can download apps and use them on any Windows device.
For More Details please visit: http://msdn.microsoft.com/library/windows/apps/hh464920.aspx