If speaking to a non-technical audience I would simply describe that as "3D space". Because in doing so you are not making up new terminology for a part of the interface that already has a name, nor are you describing it inaccurately.
The 3D Viewport's job is to portray objects in three-dimensional space, so by focusing on the content instead of the part of the interface displaying it you can keep them focused on what's most relevant.
On the other hand, if that part of the interface is a detail that is relevant to the subject matter, will be brought up repeatedly, and may contribute to their understanding of your presentation, then it may be worth simply introducing it: "This part of the screen is called the 3D Viewport".
(Note that "view port" is spelled as one word when used within the context of Blender.)