Dimensionality

Geometrical figures that are flat such as triangles, disks (circles and ellipses), and quadrilaterals are two-dimensional figures. These figures extend in two directions, sometimes called length and width. Two-dimensional figures have an area.

Flat figures can be placed in a coordinate plane, where the position of each point can be identified using two numbers.

A three-dimensional figure is a geometrical figure that has three dimensions — length, width, and height. Unlike two-dimensional figures, three-dimensional figures have height, which can also be referred to as thickness or depth.

All three-dimensional figures occupy space, which is measured in terms of volume. Some examples of basic three-dimensional figures are spheres, cones, pyramids, cubes, and prisms.

These figures can be placed in a coordinate system where the position of every point can be identified using three coordinates. Three-dimensional is often written as 3D, so these figures are commonly called 3D figures.