A polygon is a flat (two-dimensional) shape made up of straight line segments that are connected end-to-end, forming a closed figure.

Key points:

• The sides must be straight (no curves).
• The sides meet only at their endpoints (called vertices).
• It must form a closed shape — no open gaps.
• Examples: triangle (3 sides), rectangle (4 sides), pentagon (5 sides), hexagon (6 sides), etc.

If you’d like, I can also explain the different types of polygons, like regular vs. irregular, convex vs. concave, in a simple chart.