The turbocharger is a common component in most automotive engines. It consists of a compressor and turbine connected by a common shaft that spins at high speed when driven by the engine. The compressed air produced from the compressor provides more oxygen for efficient combustion, resulting in greater power output from the cylinders. This increase in performance gained by forced air is called the "turbo effect".
The compressor side of a turbocharger is driven by exhaust gas from the engine, which spins its shaft via a series of gears (usually spur gears). The turbine side has no connection to the engine but rather sucks in and compresses air as it passes through. This causes a rise in intake pressure. The greater the pressure, the more power output.
The turbocharger is fitted with a set of vanes that control the degree of the exhaust gas flowing to the turbine side. In some cases these are constructed from exotic metal alloys that allow them to warp under temperature differentials, thus moderating and controlling back pressure (which increases performance).