Modern UI refers to the user interface design philosophy developed by Microsoft, concentrating on clean lines, large fonts and the display of simple information.
Modern UI was originally named "Metro UI", but a dispute over the name "Metro" caused a name change to "Modern".
Later, the Zune desktop application introduced clean, square tiles as a central theme of navigation, an idea which which later grew into "Live Tiles".
Now, Modern UI with Live Tiles is the main focus of the design of the Start screens/menus of Windows Phone 7, Windows 8, Windows 8.1, Windows Server 2012, and "Home" on Xbox 360 and Xbox One. Windows 10 still has live tiles but no longer uses the Modern Design language.