2D Shapes

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

A flat blue sheet representing a 2D plane with length and width but no thickness

A piece of paper feels flat, but it still has a tiny bit of thickness. A true 2D shape is perfectly flat and has absolutely no thickness.

Regular Polygons

A polygon is a 2D shape with straight sides.
A regular polygon has all sides equal and all angles equal:

Regular 3-sided polygon (equilateral triangle)
Triangle - 3 Sides		 Regular 4-sided polygon (square)
Square - 4 Sides
Regular 5-sided polygon (pentagon)
Pentagon - 5 Sides		 Regular 6-sided polygon (hexagon)
Hexagon - 6 sides
Regular 7-sided polygon (heptagon)
Heptagon - 7 Sides		 Regular 8-sided polygon (octagon)
Octagon - 8 Sides
Regular 9-sided polygon (nonagon)
Nonagon - 9 Sides		 Regular 10-sided polygon (decagon)
Decagon - 10 Sides
More ...

Irregular Polygons

These are 2D shapes, and they are polygons, but irregular because their sides or angles aren't all equal:

Irregular 4-sided polygon (quadrilateral)
Quadrilateral
Any 4 sided 2D shape		 Irregular 4-sided polygon with right angles (rectangle)
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, a perfectly round 2D shape with no corners.
Circle		 Ellipse, an oval-shaped 2D curve.
Ellipse
And many more!

A 3D square prism showing width, height, and depth

3D Shapes

There are plenty of 3D shapes too!

6699, 2736, 6705, 6711, 1746, 1748, 1749, 3220, 3221, 3222
Polygons (more detail) 3D Shapes Geometry Index