Impossible.
A star is a star because of the compression of hydrogen in it's core. Being a donut, it would be without a core and thus could not be a star.
a torus
A doughnut (donut).
No. Tornadoes are typically column of funnel shaped.
long johns
erythrocytes
The donut shaped radiation belts around the Earth are called the Van Allen Belts. There are similar belts around every planet with a magnetic field.
diameter
Bagel
Red corpuscles fit this description,
A puff of smoke that's in a shape of the exhaust pipe A gasket/seal that is shaped like a donut. They are used between the manifold and the exhaust pipe.
They need not be. Many electromagnets are circular disks or toroidal (donut shaped). Bar magnets, not surprisingly, are bar shaped - often with a rectangular cross section.
Van Allen belts. :)