Turbo, as in Hyper 21 turbo, refers to a turbine shaped fan in the crankcase, spinning with the crank shaft. It is supposed to boost air flow through the engine. Nitro engines with turbo plugs are sometimes called turbo or turbo head. Ported engines are not called turbo that I know of. And outside of rc, turbo means turbocharged, which is an exhaust driven compressor that forces extra air into an engine. But turbo can also refer to turbine, when talking about aircraft, as in turbo-prop. That is a turbine engine powered propeller aircraft. And the last thing I can think of is the GM automatic transmission, called the turbo-hydramatic, known as a turbo 200, turbo 400, etc. Got that?