In mathematics, the three-dimensional shape commonly compared with a doughnut is a torus.
A torus is a surface generated by revolving a circle around an axis in the same plane that does not intersect the circle. The familiar solid doughnut is the everyday example of a torus, although a torus can have many proportions and need not resemble a pastry closely.
The torus is important in geometry and topology. Topologically, it has one central hole, and its surface differs from that of a sphere because loops around and through the hole cannot all be shrunk to a point in the same way.
The word comes from Latin torus, meaning a swelling or cushion. In science and engineering, toroidal shapes appear in objects such as magnetic cores, inflatable tubes, and some fluid vortices.