3D shape

A two-dimensional shape is flat, whereas a 3D shape has length, width and height. The complete outside boundary of a solid is its surface. A flat part of this surface is called a face, and every face is itself a 2D shape.

A 2D shape is flat, but a 3D shape extends in three directions. When describing a solid, look at its outside and separate three kinds of feature: flat faces, curved surfaces and the places where flat faces meet.