What is "convex polygon"

n. a polygon such that no side extended cuts any other side or vertex; it can be cut by a line in at most two points [ant: concave polygon]

A convex polygon is a simple polygon (not self-intersecting) in which no line segment between two points on the boundary ever goes outside the polygon. Equivalently, it is a simple polygon whose interior is a convex set. In a convex polygon, all interior angles are less than or equal to 180 degrees, while in a strictly convex polygon all interior angles are strictly less than 180 degrees.

A simple polygon which is not convex is called concave.