Medial axis
Named by 2 essays across one field — each of them below, with the objects they name alongside it.
Also named here as skeleton — the same set of essays touches all of them, so they are one junction rather than several.
The skeleton inside a shape
Take the Voronoi diagram not of a handful of points but of a shape's whole outline: the points inside the shape that have two nearest points on its edge. What comes out is a skeleton — a thin branching tree that describes the shape and, with one number attached to each point, rebuilds it exactly. It is also where fires lit all round the edge would meet, and it is violently unstable: a tooth too small to notice grows a branch several times its own size.
A skeleton that ignores small teeth
The medial axis of a shape grows a branch to every bump on its outline, however small, so a scanned shape has a skeleton made mostly of noise. Keep only the points of the axis whose nearest boundary points are spread across a circle of radius at least λ, and the branches to bumps smaller than about 2λ disappear while the real skeleton stays. That λ-medial axis moves only a little when the outline wobbles by much less than λ — and the price is λ itself, a size below which a feature is declared not to exist, which can even cut a shape's skeleton in two.
Named alongside it
The objects these essays reach for when they reach for this one.
SkeletonVoronoi diagramCircleDelaunay triangulationDistance functionHausdorff distanceInstabilitySamplingScaleStability