It's now been officially announced and confirmed. Windows 8 is the official name for the next version of Windows and will feature four editions: Windows 8, Windows 8 PRO, Windows RT (Windows on ARM or WOA), and Windows 8 Enterprise. There will also be a language-only edition for China and emerging markets.
"Windows 8 is the official product name for the next x86/64 editions of Windows," Microsoft stated in the official blog post. Windows 8 will feature two editions for 32bit and 64bit PCs and tablets. Windows 8 and Windows 8 Pro, as well as a local language-only edition of Windows 8 for emerging markets and China. Windows 8 Pro is designed for enthusiasts and business users and will feature encryption, virtualization, PC management and domain connectivity. Windows Media Center will be available via a "media pack" addon for Windows 8 Pro. Windows 8 RT is also known as Windows on ARM and will be pre-installed on PCs and tablets powered by ARM processors. "Windows RT will include touch-optimized desktop versions of the new Microsoft Word, Excel, PowerPoint, and OneNote," Microsoft added. Windows 8 Enterprise includes all the features of Windows 8 Pro plus features for IT such as PC management and deployment, advanced security, virtualization, and new mobility scenarios.
Source: Windows Team Blog