Definition of black holes:
(n) :
(physics) A region of spacetime that exerts a gravitational pull strong enough that no matter or energy, not even light, can escape it.
(n) :
(figuratively) A void into which things disappear for good; an inscrutable area or subject.
(n) :
(Internet, often attributive) A place where incoming traffic is silently discarded.
(n) :
(programming) A bit bucket; a place of permanent oblivion for data.
(n) :
(aviation) A dangerous optical illusion that can occur on a nighttime approach with dark, featureless terrain between the aircraft and a brightly-lit runway, where the aircraft appears to the pilots to be higher up than it actually is, potentially triggering a premature or overly-steep descent and a crash short of the runway.
(n) :
A place of punitive confinement; a lockup or cell; a military guardroom.