Tom Warren on The Verge:
Office 2010 introduced the idea of a Professional Plus edition, and it appears this could be making its way to Windows along with the following SKUs:
Windows 8 Starter edition
Windows 8 Home Basic Edition
Windows 8 Home Premium edition
Windows 8 Professional edition
Windows 8 Professional Plus edition
Windows 8 Enterprise Edition
Windows 8 Ultimate edition
Windows 8 ARM edition