Turbocharging
Using exhaust energy to force more air into an engine, so a smaller engine can deliver more power.
A turbocharger is a turbine spun by the engine's own exhaust flow and connected to a compressor that pushes extra air into the cylinders. With more air, the engine can burn more fuel per cycle, so it makes more power without growing in size.
Fueleconomy.gov states that turbochargers increase engine power, which allows manufacturers to use smaller engines without sacrificing performance, or to increase performance without lowering fuel economy. Pairing a smaller engine with a turbocharger is often called "downsizing."
Fuel consumption figures from an official test cycle are laboratory results. Your own consumption depends on how the car is driven and loaded, so treat the rated figure as a comparison tool rather than a prediction. The pause before a turbocharger delivers full boost is known as turbo lag.
Battery electric cars have no combustion engine, so turbocharging does not apply to them.