The correct term I believe is Windows 8 Modern UI apps which can be complied to target x86, ARM or both.
So very OT but here goes
AFAIK the API is WinRT, the O/S is Windows RT and the style is called Windows Modern or ModernUI but never Metro (except by everybody). No one can muddy the waters like MS can.
Edit: Ninja'd, so there are others who deal with this mess every day here too....