black boxˌblack ˈbox noun [countableC] informal1an electronic unit that records information on an aircraft about its height, speed etc. If the plane crashes, the black box can be examined to find the causesData from the black box recovered from the destroyed helicopter has been played back satisfactorily.
2a machine that works in a secret way that is not normally explained to peopleWe found out what formulas were inside the black boxes that firms used to determine when to set off computer-driven program trades.