Three points always lie on one (or more, for collinear points) planes, but four or more may not. Is there an application for polygons (with more than three vertices) that do not have vertices that lie on a plane? Do conventional formulas like the sum of internal angles still apply? And is there a term for such polygons?
The only mentions I've found on Google are for CAD software, and how to triangulate them to make them planar.
It may be not exactly what you've searched for, but http://www-video.eecs.berkeley.edu/papers/avz/Two-dimensional%20IEEE%20SP%2092.pdf.