Black box. What is it?
A "black box" (they are actually bright orange, to facilitate their being found after a crash) is an audio recording device in the cockpit of an airplane or helicopter. It records the conversation of the pilots during a flight, so if something goes very wrong, investigators can use the black box recording to determine what happened. Although these devices were originally called black boxes for a different reason, they are also an example of a black box according to the meaning above, in that it is of no concern how the recording is actually made.