what is a torus
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.he flat torus is a torus with the metric inherited from its representation as the quotient, R 2 / L, where L is a discrete subgroup of R 2 isomorphic to Z 2. This gives the quotient the structure of a Riemannian manifold.