Torus
![A torus](/Images/godic/202501/19/Torus.svg2424.png")
![As the distance to the axis of revolution decreases, the ring torus becomes a horn torus, then a spindle torus, and finally degenerates into a sphere.](/Images/godic/202501/19/Sphere-like_degenerate_torus2424.gif")
![A torus is the product of two circles, only one of which is shown in this diagram. The red circle is swept around an axis, which is not shown. R is the radius of the magenta circle; r is the radius of the red one.](/Images/godic/202501/19/Torus_cycles.svg2424.png")
![R > r: Ring torusR = r: Horn torusR < r: Spindle torusBottom-halves and cross-sections of the three classes](/Images/godic/202501/19/Standard_torus-ring2424.png")
In geometry, a torus (plural tori) is a surface of revolution generated by revolving a circle in three-dimensional space about an axis coplanar with the circle. If the axis of revolution does not touch the circle, the surface has a ring shape and is called a torus of revolution.