This discussion confused me until I looked up "torus" and found there are really two different definitions of this word:

(a) a SURFACE generated by a circle rotated about a coplanar axis outside the circle. Examples: an inner tube or a swimming tube. (This is what's meant by "a hollow torus" in the description).

(b) a SOLID generated by a circular lamina rotated about a coplanar axis outside the lamina. Example: a bagel or an annular gasket. I was thinking of this one, and the descriptions made no sense at all.

Now it all makes sense.

Hmm. I thought before this that I knew what a torus was...