What is a Turbo-charger?

 Turbo-charger  is a turbine-driven forced induction device that increases an internal combustion engine's efficiency and power output by forcing extra air into the combustion chamber.
              The difference between a turbocharger and a conventional supercharger is that a supercharger is mechanically driven by the engine, often through a belt connected to the crankshaft, whereas a turbocharger is powered by a turbine driven by the engine's exhaust gas.

The above is the Typical outline of the working of Turbo-charger.

                      In aircraft engines, turbocharging is commonly used to maintain manifold pressure as altitude increases.Since atmospheric pressure reduces as the aircraft climbs, power drops as a function of altitude in normally aspirated engines. Systems that use a turbocharger to maintain an engine's sea-level power output are called turbo-normalized systems. Generally, a turbo-normalized system attempts to maintain a manifold pressure of 29.5 inches of mercury (100 kPa).

         The turbocharger has three main components:

1. The turbine, which is almost always a radial inflow turbine (but is almost always a single-stage axial inflow turbine in large Diesel engines)
2. The compressor, which is almost always a centrifugal compressor
3. The center housing/hub rotating assembly.

                                                                                       (src: wikipedia)