What is a key characteristic of a concave polygon?

A concave polygon is defined by having at least one interior angle that is greater than 180 degrees. This unique characteristic causes part of the polygon to "cave in" toward the interior, creating a distinctive shape compared to a convex polygon, where all interior angles are less than 180 degrees and every vertex points outward.

This defining trait means that in a concave polygon, if you were to draw a line between two points on the boundary of the polygon, that line segment would lie outside the polygon at some point, which is not the case for convex polygons. The presence of that single angle greater than 180 degrees is what categorizes the shape as concave, making it very important for identifying such polygons in geometry.