torus

Imagine a doughnut. That gives you the basic idea of a torus. It is a geometric shape made when a circle is spun around a line outside the circle, creating a smooth ring-shaped surface. You can picture it in an inner tube, a life preserver, or other objects with a rounded hole in the middle. The word is used most often in mathematics, geometry, and physics when people talk about shapes, surfaces, or fields that have this form.

A torus is a surface of revolution formed by rotating a circle in three-dimensional space around an axis that lies in the same plane as the circle but does not cut through it. If that sounds technical, think of it this way: take a circle and spin it around a nearby line outside it, and the shape traced out is a torus. The most familiar example is a doughnut-shaped surface, and an inner tube is another easy picture.

In mathematics, the torus is important in geometry and topology, where it is studied as a classic example of a curved surface with a hole in the middle. Mathematicians describe different kinds by changing the size of the hole and the thickness of the ring. In physics and engineering, toroidal shapes appear in places such as tokamaks, where magnetic fields are arranged in a doughnut-like form to help control hot plasma. The term is also used more generally for anything that has this ringed, rounded shape.

The word "torus" comes from Latin, where it originally referred to a swelling or rounded bulge. You may not hear it much in daily conversation, but it is a useful word whenever someone needs to describe a doughnut-like surface clearly and exactly. So the next time you see a doughnut or an inner tube, you will have a precise name for that familiar shape.