On the CDi it will be a turbo. Both are types of compressor, used to get more air into the engine, more air = more oxygen, more oxygen allows for more fuel which gives more power for the cubic capacity of the engine, also known as forced induction.
A turbo charger is driven by the exhaust gases exiting the engine, a supercharger or kompressor is belt driven from the crankshaft pulley. A turbo charger is simpler but you get what is known as lag until the pressure builds. A super charger is more instant.