2D shapes only have two dimensions; these dimensions are length and width.

A polygon is a 2D shape that is made up of 3 or more straight lines. A circle is not a polygon, and this is because a circle does not have straight side. A semi-circle is also not a polygon, and this is because the curve on the semi-circle is curved and not straight.

We give polygons a name based on the number of sides that the shape has.

Here are a few polygon names that you will come across:

All of these shapes (except a nonagon) are shown below.

A polygon is a 2D shape that is made up of 3 or more straight lines. A circle is not a polygon, and this is because a circle does not have straight side. A semi-circle is also not a polygon, and this is because the curve on the semi-circle is curved and not straight.

We give polygons a name based on the number of sides that the shape has.

Here are a few polygon names that you will come across:

- Triangle – 3 sides shape
- Quadrilateral – 4 sides shape
- Pentagon – 5 sides shape
- Hexagon – 6 sides shape
- Heptagon – 7 sides shape
- Octagon – 8 sides shape
- Nonagon – 9 sides shape
- Decagon – 10 sides shape

All of these shapes (except a nonagon) are shown below.

The name of the polygon just refers to the number of sides that the polygon has. There are two different types of polygons; regular and irregular polygons. Regular polygons have sides that are of the same length and angles that are of the same size. Regular triangles are known as equilateral triangles and regular quadrilaterals are known as squares. The other regular polygons just have regular in front of the polygon name. For example, a regular pentagon is just called a regular pentagon. All of the polygons in the diagram above were regular.

Below is an example of a regular and irregular pentagon.

Below is an example of a regular and irregular pentagon.