The new Windows 8 UI is officially called Windows 8 Modern as defined in this Tech Target article
QUOTE: Microsoft Windows 8 Modern (formerly called Metro) is the user interface(UI) initially released with the Windows 8 operating system (OS). Modern uses bright, high-contrast color schemes and arrays of large icons (called “live tiles”) to create a simple design aesthetic. Modern focuses on reorganizing applications and tasks into intuitive groupings, with icons that use actual content rather than static graphical buttons. For example, a photo-viewing application would actually display the user’s photos in a live tile called “Photos.” Similarly, pictures and avatars representing user’s various phone and email contacts would appear in rotating mosaics across the “Contacts” live tile.