Hoop conjecture (K.S. Thorne, 1972):

The conjecture (as still unproven, though there is substantial evidence to hold up it) that a nonspherically compressed, nonspherical object, will only form a black hole while all parts of the object lie within its event horizon; i.e., while a "hoop" of the event horizon circumference can be rotated in all of the directions and will totally enclose the object in question.