It is a hexagon with a reflex angle.
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It is concave because it is going in so it is going in the cave
concave, equilateral
You start creating a concave hexagon from four triangles by placing the smallest triangle in the middle to serve as a base for the other three. Line up the bases on each triangle with the sides of the smallest one to end up with six sides forming a concave hexagon.
ref
A regular hexagon and 3 classes of convex hexagons, plus concave hexagons will tessellate.