Toroid

The name for any doughnut-shaped body. [Mathematics: a surface generated by a closed curve rotating about, but not intersecting or containing, an axis in its own plane.] The shortened popular name for the doughnut-shaped (toroidal) transformers used in some audio equipment. Toroidal transformers tend to cost more, take up more space, and are often heavier than other designs, but the shape reduces magnetic fields both leaving or entering the transformer, which makes them desirable in many audio applications due to reduced hum induction.