Concave polygon

A simple polygon that is not convex is called concave,[1] non-convex[2] or reentrant.

None of these three statements holds for a convex polygon.

As with any simple polygon, the sum of the internal angles of a concave polygon is π×(n − 2) radians, equivalently 180×(n − 2) degrees (°), where n is the number of sides.

A polynomial-time algorithm for finding a decomposition into as few convex polygons as possible is described by Chazelle & Dobkin (1985).

The convex hull of the concave polygon's vertices, and that of its edges, contains points that are exterior to the polygon.