A concave polygon is a polygon that is not convex.
A simple polygon is concave iff at least one of its internal angles is greater than . An example of a non-simple (self-intersecting) polygon is a star polygon.
A concave polygon must have at least four sides.
Portions of this entry contributed by David Terr
More things to try:
Weisstein, Eric W., with contributions by David Terr. "Concave Polygon." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/ConcavePolygon.html
. An example of a non-simple (self-intersecting)
polygon is a star polygon.
