That sealed piece of replaceable equipment in electronics is referred to as black box.
The human mind is envisioned as a black box by those in the field of philosophy and psychology as to what they learned in the school of behaviorism.
You would often hear black box in aircraft crash reports as this is referred to as the flight data recorder and cockpit voice recorder in the field of aviation.
Software engineers and computer programmers use black box testing to check if the output of a program delivered as predicted based from specific inputs.
In physics, a system with anonymous internal structure is called a back box.