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Black Boxes from WikiPedia:

Black box is a technical term for a device, system or object when it is viewed in terms of its input, output and transfer characteristics without any knowledge required of its internal workings. Almost anything might occasionally be referred to as a black box: a transistor, an algorithm, humans, the Internet.

The opposite of a black box is a system where the inner components or logic are available for inspection (such as a free software/open source program), which is sometimes known as a white box, a glass box, or a clear box.

The modern term "black box" seems to have entered the English language around 1945. The process of network synthesis from the transfer functions of black boxes can be traced to Wilhelm Cauer who published his ideas in their most developed form in 1941. Although Cauer did not himself use the term, others who followed him certainly did describe the method as black-box analysis. Belevitch puts the concept of black-boxes even earlier, attributing the explicit use of two-port networks as black boxes to Franz Breisig in 1921 and argues that 2-terminal components were implicitly treated as black-boxes before that.

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