A fork of Rural Dictionary
During concerts fans will flail their cellphones and light sticks as the artist(s) performs, creating an "ocean" of light from the perspective of the performer. A "black ocean" is a trend in K-pop (Korean Pop or music) where the audience turns off their light sticks and cellphones as a show of lack of support to the current group onstage. When done collectively, it appears to the performers as a "black ocean" due to the lack of lights from the audience. Usually only happens in extreme cases. Then again, "extreme" is a subjective word when it is put together with the craziness and stupidity that is the hardcore fans of K-pop.
SNSD and EXO were victims of the Black Ocean during the start of their careers.