Plug in performance refers to the modification of a vehicle’s engine control system, or software to achieve performance gains. This is usually performed with aftermarket engine management systems and engine chips. A scanner connects to the engine control system and, with the assistance of the chip, is able to modify a number of factory set options. Such as the air fuel ratio, which can directly affect a vehicle’s power output. Plug in performance gets its name because the device used to control the system plugs into the vehicle’s diagnostics port.
For more info, see What Does an Engine Tuning Chip Do?