Basically it's only partially brake-by-wire system. "By-wire" means that the control input is physically disconnected from the mechanical end device we want to control. There is no physical linkage between the control input and the mechanical device on the car except electical wire. In planes (fly-by-wire) the pedals and stick are attached by wire (electrical wire) to a computer that measures the input and then translates that to the control surfaces. So, translate this to cars (both road and racing) and you get things like "throttle-by-wire" which has been in Formula 1 for quite some time. Instead of the throttle being connected directly to the engine, it's connected to a computer. It measures input, takes other things into account and applies that to the engine throttle. When you hear things like "throttle mapping" this is what is being referred to. For instance when the car is in rain mode, the throttle response is slower to prevent wheel spin due to lower grip. In dry running, the throttle response is much faster.