Black noise has various definitions — as far as we are aware none of them are official. Some common definitions are listed below:
(1) Silence, no noise at all.
(2) Noise with a 1/fβ spectrum, where β > 2.
(3) Noise which has zero energy at most frequencies but contains occasional random spikes.
(4) The noise created by active noise control systems, designed to cancel existing noises.
(5) Ultrasonic white noise, i.e. white noise which is at a frequencies too high to hear but which can still affect the environment.
Main page: Noise Colours