geometry, a torus (pl. Tori) is a surface of revolution generated by
revolving a circle in three dimensional space about an axis coplanar with the
circle, which does not touch the circle. Examples of tori include the
surfaces of doughnuts and inner tubes. The solid contained by the surface is
known as a toroid. A circle rotated about a chord of the circle is called a
torus in some contexts, but this is not a common usage in mathematics. The
shape produced when a circle is rotated about a chord resembles a round
cushion. Torus was the Latin word for a cushion of this shape.