It is a device, system or object with input and output. There is no knowledge of its internal workings. The way it works is "opaque" (black). Almost anything might be referred to as a black box: a transistor, an algorithm, or the human brain.
Ashby expains that the term arose when a decision had to be made about opening an engineering box. The question was whether to return the box for repair, or just scrap it. Could this be decided without opening the box? There can be many reasons why a complex system cannot be repaired in the field, and even opening up some systems is a big deal. The question also comes up in surgery on brain damage patients. The more that can be discovered before operating, the better.p86
The opposite of a black box is a system where the inner components or logic can be seen. It is sometimes known as a clear box, a glass box, or a white box.
- Ashby, W. Ross 1956. An introduction to cybernetics. London: Chapman & Hall, chapter 6 The black box, p86–117.