noun

1. A topological space which is a product of two circles.

   “A 4-variable Karnaugh map can be thought of, topologically, as being a torus.”

2. The standard representation of such a space in 3-dimensional Euclidean space: a shape consisting of a ring with a circular cross-section: the shape of an inner tube or hollow doughnut.

3. (in combination, n-torus, 4-torus, etc.) The product of the specified number of circles.