blackout

The complete loss of electrical power in a particular area. Blackouts can result from a natural disaster, a manmade catastrophe, or simply from an excess of energy demand over supply. (Compare brownout.)

Obliterate with black, as in crossing out words on a page or print on a screen. For example, They have blacked out all the obscene words in the subtitles to make this movie suitable for youngsters. This usage may be derived from an earlier meaning, “to stain or defame,” which dates from the 15th century (and probably alludes to “blackening” a person's reputation). [Mid-1800s]

Extinguish all lights. For example, The whole town was asleep, as blacked out as London during the war. In the early 1900s this expression alluded to the lights in a theater, but from about 1940 on it meant darkening an entire city to hide it from enemy bombers.

Lose consciousness, faint; also, experience a temporary loss of memory. For example, I couldn't remember a single note of the music; I blacked out completely, or The accused man claims he blacked out after his first drink. This usage is thought to have originated with pilots, who sometimes fainted briefly when pulling out of a power dive. It soon was transferred to other losses of consciousness or memory. [c. 1940]