a ring-shaped surface generated by rotating a circle around an axis that does not intersect the circle
a coil in the shape of a ring, in geometry a torus
a cylindrical shape that capacitors to wound with wire is create inductance
a doughnut-shaped object enclosed by a torus
A round magnetic core structure in the shape of a ring, often referred to as a doughnut core due to the similarity in shape.
A toroid is a doughnut-shaped object whose surface is a torus. Its annular shape is generated by revolving a circle around an axis external to the circle.