Control of vehicle functions via electronically-transmitted signals
When the throttle opening and air/fuel mixture is controlled by electronics rather than by mechanical linkage.
Drive-By-Wire means that one or more of the primary vehicle systems is operated by electronic controls instead of traditional mechanical linkages. An example of a "drive-by-wire"system is an electronically controlled throttle in which a computer controls the relationship between the accelerator pedal and throttle position to optimize actual throttle response, which can increase fuel economy, improve driveability and reduce emissions.
Drive-by-wire means that commands from the vehicle driver are no longer passed on to the relevant devices mechanically but electronically. The commands (e.g. steering or pushing on the accelerator) are received by sensors, processed by a computer, and then passed on to the relevant assemblies (e.g. the steering system, engine, transmission or brakes) via electric motors. Mechanical linkages like the steering rod and hydraulic brakes are not needed in drive-by-wire vehicles.
Electronic as opposed to traditional mechanical actuation of some component; for instance, of a throttle. Sensors and actuators replace levers, cables or other mechanical linkages.