A torus (plural: tori or toruses) is a tube shape that is similar to the surface of a doughnut or an inner tube. In geometry, a torus is obtained by rotating a circle in three dimensional space. To make a torus, the circle is rotated around a line (called the axis of rotation) that is in the same plane as the circle. Usually the line does not touch the circle, so the torus has a hole through the center, and the torus is called a ring torus. For a ring torus, the axis of rotation passes through the center of the hole. 