Dictionary

A torus (pl. tori) is a surface shaped like that of a donut or bagel.

It is possible to define analogous geometric objects, all of them finite in extent and closed in upon themselves, with more dimensions than two. These are also known as tori; whenever it is necessary to indicate such an object’s dimensionality, one can simply add a qualifier to the name: The donut surface is a two-torus (two-dimensional), its three-dimensional analogue is a three-torus, and so on.