According to sources from Microsoft, anything currently or formerly known as a Metro-Style application (regardless of the hyphen) will henceforth be referred to as a Windows 8 application. In addition to that, references to the Metro user interface will be replaced by a Windows 8 user interface and instead of using Metro design, Microsoft and everybody else involved with the project will use the term Windows 8 design.
This news doesn't seem to be a big secret though as some OEMs seem to have gotten the message. Lenovo's new promo page for the new Windows 8 Thinkpad Tablet 2 has no mention of the word Metro anywhere on it. Instead, the heading Windows 8 apps is used. However, some at Microsoft are still using the Metro term in certain situations.
Some divisions at Microsoft were still using Metro to refer to the tiled interface with bold Segoe-font typographic elements. Metro became a nickname to refer to the new look and feel of Windows 8, as well as a way to refer to apps built using the new WinRT programming interface. It also seems as if Microsoft is going to use the Windows 8 name change with its Windows Phone as well. That means the Metro interface on Windows Phone will now be known as the Windows 8 interface.
Source: ZDNet - Microsoft: Don't call it Metro. Call it 'Windows 8'