Point B on blue bar of an ellipse mechanism traces an ellipse (in black). Three other curves are traced by the points on the yellow bar that has revolution joint with the blue bar at B and prismatic joint with the pink part.
They are considered as the result of the black ellipse deformation with constant distance along the normals to the black ellipse.
They are equidistant or parallel curves with respect to the black ellipse.
This method of forming curves is used in designing and manufacturing of profiles, non-circular wheels, cams etc.