As of today, Microsoft also christened the desktop version of its Office suite as "Office 2016." (Until today, that suite was known only by its codename, "Office 16.")
The desktop version is going to be more fully featured, most likely include additional Office apps as part of that suite, and work on the desktop in Windows 10.
As Microsoft officials revealed yesterday, the Office for Windows 10 suite will be preinstalled for free on Windows Phones and small (under eight-inch) tablets running Windows 10. They will be available for download from the Windows Store for Windows devices with larger screen sizes.
As of today, we don't have official word if these downloadable touch-first versions will be free or require an Office 365 subscription to unlock the full set of features -- as is the case with Office on iPad and Office on Android tablets.
I previously heard from my sources that the first public preview of Office for Windows 10 would be available in February 2015. Today's blog post says the Office universal apps will be available with "the Windows 10 Technical Preview in the coming weeks." I'm taking this as meaning it will be in February as part of the first Windows 10 mobile preview (for Windows Phones and small Intel- and ARM-based tablets).
(A quick note on naming: Microsoft officials have decided to brand all versions of Windows 10 plain-old "Windows 10." But the Windows 10 version that is built for phones and tablets isn't the same as the one for the desktop, so to distinguish them, I will keep calling the phone/tablet SKU "Windows 10 mobile.")
Today's post notes that general availability for the Office for Windows 10 suite will be "later this year." My sources have said it will be generally available at the same time as Office 2016, which Microsoft officials previously stated Office 16 would be in the second half of calendar 2015.