Rectilinear and Curvilinear
Definitions:
Rectilinear- characterized by straight lines.
Curvilinear- consisting of or bounded by curved lines: a curvilinear figure.
Examples:
Rectilinear- http://mathworld.wolfram.com/RectilinearCrossingNumber.html
Curvilinear- http://www.marklaurence.com/articles/discourse_on_curves.html
Read more about this topic: Shape And Form (visual Arts), Categories