A torus is shape defined as the shape formed by rotating a circle around an axis coplanar with the circle. The resulting shape will have one of three forms: a ring torus, in which the axis if revolution does not touch the circle; a horn torus, in which the circle is tangent to the axis; and a spindle torus, in which the axis is a chord of the circle. There are many real examples of the torus shape around the house: donuts, bundt cakes, life preservers, bicycle inner tubes and cushions.
The word torus is unchanged from Ancient Rome: the Latin word torus was a cushion. In architecture, the base of many columns contains a toroid, which acts as a ‘cushion’ for the column.
GIF of torus shapes courtesy Kieff who created the GIF and released it to the public domain. Thank you Kieff for such a beautiful image, and thank you for sharing your work with the world!
Image of The Column of Trajan, Rome, Dedicated in A.D. 113 to commemorate the emperor’s victory over the Dacians courtesy Roger Ulrich under a Creative Commons 3.0 license. Thank you Roger for releasing your word to Creative Commons.