black box

noun
RareNot in standard dictionaries
1

A flight recorder; the brightly colored cockpit voice recorders and flight data recorders in an aircraft designed to aid in determining the cause of an accident.

2

Any similar device on motor vehicles, such as rail event recorders and ship trip recorders.

3

A theoretical construct or device with known input and output characteristics but unknown method of operation.

4

A device used in phreaking that prevents the calling party from being billed for the call placed.

5

A type of theater characterized by a lack of decoration or complex mechanisms.

6

Synonym of football (“the leather briefcase containing classified nuclear war plans which is always near the US President”)

#informal