the tag windows-10-desktop is for questions concerning application development for the Windows 10 Desktop. Windows 10 Desktop development uses the Win32 API and provides a user interface similar to a traditional Windows UI that supports and may require the use of a keyboard and mouse. Along with this tag should be a tag indicating the language being used and the platform such as .NET. This tag is not used for posts concerning WinRT application development.
Windows 10 comes in three main flavors: Windows 10 Desktop, Windows 10 Mobile, and Windows 10 IoT. Development can be done in a wide variety of languages with several different target processors as well as the different target versions of Windows 10.
The Windows Desktop, Win32, uses the Windows 10 version of the Win32 API which contains functionality that is unavailable in the WinRT in order provide the security of a protected environment for WinRT. The most common processor target is x86 or x64 CPUs.
See the discussion and links in How to: Use Existing C++ Code in a Universal Windows Platform App.
The Windows Runtime, WinRT, with Universal Windows Platform applications allows for a code once, compile many for specific target. A UWP application can be built to target one of several different processors (x86, x64, ARM) as well as any of the versions of Windows 10 (Windows 10 Desktop, Windows 10 Mobile, and Windows 10 IoT).