The term 'shape of a doughnut' is often used to describe the geometric shape known as a torus, which has five letters. A torus is a three-dimensional shape that is formed by revolving a circle around an axis that is coplanar with the circle. It is a closed surface with one side and no edges, and it is often used to model phenomena such as the flow of a liquid in a container. The shape of a doughnut is a classic example of a torus.