# Shape

form of an object or its external boundary

A shape is a geometric figure that can be made with mathematics. Shapes are sorted into kinds based on how the shape looks, and what the shape is made of. For example, shapes can be classified by how many dimensions they use.

Two-dimensional shapes will fit into a flat plane. Three-dimensional objects will not fit inside a plane, because they are not flat. Shapes made from other shapes of any dimension are called polytopes.

Two shapes are said to be equal, if one can be changed into the other by turning, moving, growing, shrinking, or more than one of these at once. Geometry is a section of mathematics which involves many shapes and sizes of different figures and their properties.

## 2D shapes

These are two-dimensional shapes or flat plane geometry shapes. Their sides are made of straight or curved lines. They can have any number of sides. Plane figures made of lines are called polygons. Triangles and squares are examples of polygons.

## 3D shapes

These are three-dimensional shapes. Their sides are made of flat or curved surfaces. 3D shapes are most often made of polygon faces. These 3D shapes are called polyhedra.

## 4D shapes

Four-dimensional shapes made of polyhedra are called polychorons. These shapes cannot be fully shown in the real world, but they are important ideas in geometry.