Definition of black hole noun from the Oxford Advanced American Dictionary

black hole

an area in space that nothing, not even light, can escape from, because gravity (= the force that pulls objects in space toward each other) is so strong there
(figurative)The company viewed the venture as a financial black hole (= it would use a lot of the company's money with no real result).(figurative)Thousands of people have been plunged into the black hole of unemployment.