Windows desktop applications that you buy from a third party and install via a CD or download link are known as “Windows Desktop Applications”. These will be familiar to existing Windows users.
Apps for Windows touchscreen/mobile devices were originally known as ‘Metro’ apps or ‘Windows 8-style UI apps’. They were available from the Windows Store, were optimised for small touchscreens, and were written using completely different code from regular Windows applications.
With Windows 10, the plan is for application software to be written using the same code for both Desktop Mode and Tablet Mode. These applications are known as ‘Universal apps’ or ‘UWP apps’ (Universal Windows Platform), but you may also hear the terms ‘Windows apps’ or ‘Trusted Windows Store Apps’. Figures 2-3a and 2-3b below show Microsoft Word 2016 running on Windows 10 in Tablet Mode and Desktop Mode respectively.
You can see that Word looks almost identical in both cases, only with slightly larger and more widely-spaced ribbon icons in Tablet mode. On a smaller tablet screen, Tablet mode may also auto-hide the Ribbon, to allow more space to work on documents.