The word polygon means “many angles” (Greek poly for “many”; gonis for “angle”). It is a closed figure in a plane made up of line segments (straight with no curves) that intersect only at their vertices (endpoints). In other words, no sides (lines) can touch each other except at endpoints. A polygon has the same number of sides as it has vertices.

Examples A, B, and C above are polygons, while examples D and E are not.