* Turbocharged Diesel Engine (Turbo Diesel): This refers to a diesel engine that uses a turbocharger. A diesel engine, inherently, is an internal combustion engine that uses the compression of air to ignite the fuel (rather than a spark plug like a gasoline engine). The turbocharger forces more air into the engine's cylinders, increasing the amount of fuel that can be burned and thus boosting power and torque.
* Turbocharged Engine (Turbo): This is a more general term and simply means any engine (diesel *or* gasoline) that uses a turbocharger. The turbocharger's function remains the same – to force more air into the cylinders for increased power.
In short, a "turbo diesel" is a *specific type* of "turbo" engine. All turbo diesels are turbos, but not all turbos are turbo diesels.
