black box

Short definition from Wiktionary

Noun

1. 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. 2
   Any similar device on motor vehicles, such as rail event recorders and ship trip recorders.
3. 3
   A theoretical construct or device with known input and output characteristics but unknown method of operation.
4. 4
   A device used in phreaking that prevents the calling party from being billed for the call placed.
5. 5
   A type of theater characterized by a lack of decoration or complex mechanisms.
6. 6
   Synonym of football (“the leather briefcase containing classified nuclear war plans which is always near the US President”)

Verb

1. 1
   To focus on the inputs and outputs without worrying about the internal complexity.