2D Shapes

A plane or 2D shape has 2 Dimensions (such as width and height) but no thickness.

Regular Polygons

A polygon is a 2D shape with straight sides.
To be a regular polygon all the sides and angles must be the same:

Triangle - 3 Sides	Square - 4 Sides
Pentagon - 5 Sides	Hexagon - 6 sides
Heptagon - 7 Sides	Octagon - 8 Sides
Nonagon - 9 Sides	Decagon - 10 Sides
More ...

Other Common Polygons

These are 2D shapes, and they are polygons, but not regular polygons:

Quadrilateral Any 4 sided 2D shape	Rectangle - 4 Sides All right angles
And many more!

Curved Shapes

These are also 2D shapes that are not polygons because they have curves:

Circle	Ellipse
And many more!