I have created an ellipse of constant thickness. What are the shapes for the inner and outer boundaries? I know they are not also ellipses. I was only able to draw the shape in geometry software, and do not know the formulas. Thanks.
The Wikipedia article on Parallel curve has some formulas. It also writes
the offsets of an ellipse or of a hyperbola are not rational
an ellipse has as (two-sided) offsets an algebraic curve of degree 8.
So this is going to be a pretty ugly beast of a curve, algebraically speaking, but you can probably use the parametric equation from Wikipedia for some application. As far as names go, “parallel curve to an ellipse” is likely to be as easy as it gets.