black ‧ out /ˈblækaʊt/ BrE AmE noun [countable]
1 . a period of darkness caused by a failure of the electricity supply SYN power cut
2 . a situation in which particular pieces of news or information are not allowed to be reported:
As the crisis worsened, the authorities imposed a news blackout.
3 . a period during a war when all the lights in a town or city must be turned off
4 . if someone has a blackout, they suddenly become unconscious