The letter M in BMW M5 stands for "Motorsport". BMW has been using this letter for its high-performance models since the 1970s. The first M car was the BMW 3.0 CSL, which was released in 1975. BMW M cars are built with more powerful engines and higher levels of performance than standard BMW models. They are also more luxurious and feature more advanced technology. The latest BMW M5 is the most powerful ever, with a 4.4 litre V8 engine and 600 horsepower.