The Medial axis or Voronoi Skeleton of a polygon is the set of all the points with 2 or more closest points on the polygon’s boundary. Another way of putting this is that it is the locus of the centre of all the maximal inscribed circles.
It is an important tool in computational geometry, with a wide variety of applications, from image recognition to finite element analysis. The closely related straight skeleton has also been used for generating ridge-lines for the rooves of buildings.
Here is a simple Grasshopper definition for generating the medial axis of an arbitrary 2d closed curve.
As I have written about earlier, this also generalises nicely to 3D