There exists to my knowledge no formal terminology. I have no idea where you got those terms from or why you think they are correct. Also, the answer likely depends on whom you ask: an electronics designer making screens, the OS designers, the application programmers, the front end GUI designer or the end user. All of these are likely to use very different terms.
Regarding the actual used area of a screen, it's generally referred to as active area or viewable area in the electronics industry. "Viewport" is, I suppose(?), some front-end GUI designer term. Certain OS or application programmers for specific systems might call it desktop. So there you already have very diverse terms for the same thing.
The physical size of the viewable area is generally referred to in inches for some historical reason and refers to the diagonal distance between the opposite corners. Notably, this says nothing of the actual picture quality, pixel size or resolution. A more accurate measurement of quality is the resolution, referred to in pixels.
Also, a general computer doesn't necessarily have "windows", it was something invented by Xerox back in the 1970s, but other operating systems didn't have a (window-like) GUI for a long time. To get close to actual formal terms used by the specific OS, you would have to peek underneath the hood to see what the OS calls various things internally, by studying the interface that programmers use to interact with the OS.
MS Windows for example, names the borders "border". The used area inside the window is referred to as "device context". It calls the scrollable part "range". And so on. These are internal names used for programmers and not necessarily for end users, and as such they are highly specific to that particular OS. And then the OS designers might use different names when interacting with programmers and end users.
I guess the summary of it all is that terms are specific from case to case. And therefore trying to chase down something "formal" and system-independent turns out subjective.