**Three-dimensional shapes are solid shapes that exist in three dimensions, which include length, width and depth.** The main difference between 3-D shapes and 1-D or 2-D shapes is that depth is incorporated along a third axis outside of the original 2-D plane.

Single-dimensional shapes exist only in one dimension, which means that they only possess length. Two-dimensional shapes have two dimensions, including length and width. These shapes are always flat. Examples of 2-D shapes are squares, triangles and circles. By adding an additional dimension to these 2-D shapes, many 3-D shapes can be constructed, such as cubes, pyramids and spheres. The mathematical term for a solid 3-D shape is "polyhedron."