# 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.