Microsoft recently announced that the next generation of Windows will be released by October 28th and its named Windows 8. The new feature of this release involve the Metro UI which is right from the development phase Microsoft advertised over to the community. But now we got some news that Microsoft is dropping the name “Metro UI” and renaming it as “Modern UI”. We have not got any official confirmation from Microsoft, but we can see few of the websites where Microsoft announced the upcoming events with the name Modern UI.
Windows 8 is the largest developer opportunity that combines the broad reach of Windows, our best in class developer tools and a re-imagined user experience with a new support chipset and industry-leading business terms built-in store. [more]

We can see the Modern UI name in the upcoming events that is listed in the Microsoft event page of Windows 8 ( Windows 8 Public Sector 1 Day DevCamp Series ). Microsoft, on the other hand, hasn’t confirmed the changes, leaving the us still looking for the official announcement. But it seems that employees at Microsoft have already begun using the brand “Modern UI Style” to refer to the new Windows 8 Start Screen, and “Modern UI” design in reference to its Windows 8 apps.
From Zdnet:
Anything currently/formerly known as a "Metro-Style application" (with or without a hyphen) will now be known officially as a "Windows 8 application." References to the "Metro user interface" will now be replaced by "Windows 8 user interface." And instead of saying "Metro design," the Softies and those adhering to their official guidelines will be using the words "Windows 8 design."