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The sleeping car or sleeper (often wagon-lit) is a railway passenger car that can accommodate all passengers in beds of one kind or another, for the purpose of sleeping. George Pullman was the main American innovator and owner of sleeper cars in the late 19th and early 20th centuries when railroads dominated intercity passenger travel.
The first such cars saw sporadic use on American and English railways in the 1830s; they could be configured for coach seating during the day.
A multiple-unit train (or multiple unit (MU)) is a self-propelled train composed of one or more carriages joined, and where one or more of the carriages have the means of propulsion built in. By contrast, a locomotive-hauled train has all of the carriages unpowered.
An implication of this is that all the powered carriages needs to be controllable by a single engineer or driver, which is a case of the broader concept of multiple-unit train control. In other words, all "multiple units" employ some variation of multiple-unit train control. In the broader context "unit" means any powered rail vehicle, including locomotives (that does not carry cargo) and powered cargo-carrying carriages. In the context of this article, "unit" refers specifically to the latter only (whether the cargo is passengers or some other cargo).
A railcar (not to be confused with the generic term "railroad car" or "railway car"), or motor car is a self-propelled railway vehicle designed to transport passengers. The "self-propelled railcar" refers to a railway train consisting of a single coach (or carriage, car, unit), with a driver's cab at one or both ends. In its simplest form, a "railcar" may also be little more than a railbus or motorized draisine.
Self-powered railcars were once common in North America; these "motor cars" were often called doodlebugs. Some railway companies, such as the Great Western, termed such vehicles "railmotors" (or "rail motors"). Self-propelled passenger vehicles also capable of hauling a train are, in technical rail usage, usually called "rail motor coaches".