A polygon is a closed, flat shape with straight sides. "Closed" means the sides connect all the way around — no gaps or open ends.
Triangles, squares, pentagons, and hexagons are all polygons. Circles are not — they have a curved edge instead of straight sides.
The number of sides determines the name. Three sides: triangle. Four sides: quadrilateral. Five: pentagon. Six: hexagon. And so on.
Remember
Two rules for a polygon: (1) straight sides only, (2) completely closed. Fail either rule and it's not a polygon.
Real World
A stop sign is a regular octagon — 8 equal sides, 8 equal angles. A yield sign is a triangle. Road signs are basically a geometry lesson.
Feeling ready?
Put this concept to work with a practice workout.