The term black box is a placeholder name

Placeholder name

Placeholder names are words that can refer to objects or people whose names are either temporarily forgotten, irrelevant, or unknown in the context in which they are being discussed...

 used casually to refer to a collection of several different recording devices used in transportation: the flight recorder

Flight recorder

A flight recorder is an electronic recording device placed in an aircraft for the purpose of facilitating the investigation of an aircraft accident or incident. For this reason, flight recorders are required to be capable of surviving the conditions likely to be encountered in a severe aircraft...

s (flight data recorder

Flight data recorder

A flight data recorder is an electronic device employed to record any instructions sent to any electronic systems on an aircraft. It is a device used to record specific aircraft performance parameters...

 and cockpit voice recorder

Cockpit voice recorder

A cockpit voice recorder , often referred to as a "black box", is a flight recorder used to record the audio environment in the flight deck of an aircraft for the purpose of investigation of accidents and incidents...

) in aircraft, the event recorder

Event recorder

A Train event recorder is similar to the flight data recorder found on aircraft. It records data about the operation of train controls and performance in response to those controls and other train control systems.Data storage is provided by magnetic tape, battery-backed RAM and, most recently,...

 in railway locomotive

Locomotive

A locomotive is a railway vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine, first used in the early 19th...

s, the event data recorder

Event Data Recorder

An event data recorder or EDR is a device installed in some automobiles to record information related to vehicle crashes or accidents. In modern diesel trucks, EDRs are triggered by electronically sensed problems in the engine , or a sudden change in wheel speed. One or more of these conditions...

 in automobiles, message case in ship

Ship

Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

s, and other recording devices in various vehicles.
A message case was one of the earliest forms of a black box. A written message was placed into a buoyant heavy duty water-tight metal canister

Canister

The term canister comes from Latin or Greek . It means:* Originally, from Greek καννα , a basket of woven reeds...

 and released into a body of water.