What is the collective name for MU passenger cars of the M-3, M-7, or M-8 series?

The collective name for MU (Multiple Unit) passenger cars of the M-3, M-7, or M-8 series is referred to as "M-Series Equipment." This term encompasses all the different models within that series, highlighting their specific design and operational characteristics that distinguish them from other types of rolling stock.

The designation "M-Series Equipment" indicates that these cars are intended for passenger service, specifically in commuter rail systems, and they share compatibility and features ideal for operation as part of a multiple unit train. This collective nomenclature simplifies communication regarding maintenance, scheduling, and operational procedures related to these specific types of passenger cars.

Other terms, such as "Deadhead Train" or "Freight Train," refer to different concepts entirely. "Deadhead Train" typically refers to a train moving without passengers or freight, mainly for repositioning crew or equipment. "Equipment" is too vague and can refer to any train components or rolling stock, not specifically the M-Series. Therefore, "M-Series Equipment" is the most accurate and relevant term for identifying these specific passenger cars.