What is a Turbocharger?

What is a turbocharger/turbo? A turbocharger, or turbo, is a turbine-driven forced induction device. It increases an internal combustion engine's efficiency and power output by forcing extra air into the combustion chamber. This improvement over a naturally aspirated (N/A) engine's power output is due to the fact that the compressor can force more air and proportionately more fuel into the combustion chamber than atmospheric pressure (ram air intakes) alone.
Back then, turbochargers were originally known as turbosuperchargers when all forced induction devices were classified as superchargers. Nowadays the term "supercharger" is usually applied only to mechanically driven forced induction devices.
The main difference between a turbocharger and a supercharger is that a supercharger is mechanically driven by the engine, often through a belt connected to the crankshaft. However, a turbocharger is powered by a turbine driven by the engine's exhaust gas. Compared to a mechanically driven supercharger, turbochargers tend to be more efficient, but less responsive. 
Turbochargers are commonly used on truck, car, train, aircraft, and construction equipment engines. They are most often used with Otto cycle and Diesel cycle internal combustion engines.
Example of turbocharger brand/manufacturer: Honeywell's Garret Turbo, BorgWarner Turbo System, Cummins Turbo Technology, Mitsubishi Heavy Industries, etc.

How a Turbocharger Works