Shape
A shape is an object that has some form of distinguishable external boundary, surface, or outline.
There are many ways to classify shapes; they can be classified as open or closed shapes; they can be classified by their dimensions, such as 2D or 3D.
Closed shapes
The line segments or curves forming a closed shape are continuous, meaning there is no break. The lines/curves must also form a closed region to be considered a closed shape:
Open shapes
The segments or curves of an open shape are not always connected. At least one endpoint of one side is not connected to the rest:
2D shapes
A 2D shape is a shape that lies in a plane and only has a length and a width, but no height or depth. 2D shapes are often classified as polygons and non-polygons.
Polygon
A polygon is a closed plane figure formed by line segments. The following is a list of some polygons.
| Polygon | Shape |
|---|---|
| Triangle |  |
| Quadrilateral |  |
| Pentagon |  |
| Hexagon |  |
This is not an exhaustive list of polygons. If there are n sides for a polygon, we call it an n-gon.
Non-polygon
The following is a list of some non-polygon shapes.
| Name | Shape |
|---|---|
| Angle |  |
| Circle |  |
| Ellipse |  |
| Shapes with a curve |  |
| Open 2D shapes |  |
| Parabola |  |
3D shapes
The term "3D," or "three dimensional," is a term that is used to describe space figures. They occupy space and have volume if closed. 3D shapes can be classified as polyhedrons and non-polyhedrons.
Polyhedron
A polyhedron is a closed solid whose faces are polygons. The following is one way to further classify polyhedra.
| Type | Examples |
|---|---|
| Prisms |  |
| Pyramids |  |
| Platonic solids |  |
There are many more prisms and pyramids, but only five platonic solids (regular, convex polyhedrons), the tetrahedron, cube, octahedron, dodecahedron, and icosahedron.
Non-polyhedron
A non-polyhedron is a solid that has surfaces that are fully curved or partially curved.
| Type | Examples |
|---|---|
| Partially curved surfaces |  |
| Fully curved surfaces |  |
Each shape above can be further classified. For example, a quadrilateral can be further classified as a parallelogram, rectangle, trapezoid, square, and more. Learn more about specific shapes and their classifications by navigating this website.