In science and engineering, a black box is a device, system or object which can be viewed in terms of its input and output but without any knowledge of its internal workings. Its implementation is “opaque” (black). Almost anything might be referred to as a black box: a transistor, an algorithm, or the human brain.

The opposite of a black box is a system where the inner components or logic are available for inspection, which is sometimes known as a clear box, a glass box, or a white box.

Almost all investment programs are actually a black box. That is, the investment manager may allow the investor to see the holdings, but most investment strategies have many parts and parameters that are undisclosed to the public.