A turbo-what? 8^) Do you mean a turbocharger in a car?
The word 'turbo' comes from 'turbine'. A turbine is a gizmo that converts the flow of a fluid to mechanical energy. You find them in dams, where water goes through them and turns fan blades, which in turn run an electrical generator.
In this case the turbine is connected to the exhaust of the engine. When you rev up the engine, the exhaust spins the turbine at a very high speed, like 80,000 rpm. This turbine turns a pump that compresses the air going into the engine.
Originally some cars had 'superchargers' for this purpose (and some still do, but they're rare outside of racing). A fan to compress the air going into the engine increases the compression, crams more fuel/air mixture into the engine so it gives you more power. But a supercharger is running all the time, so it uses up a lot of energy, which gives you lower fuel efficiency. A turbocharger spins up only when you need it, when you stomp on the gas to speed up. Then it spins up and compresses the intake air. So it uses energy just when you ask for it. It takes a small amount of time, half a second or so, to spin up, so there's a slight lag between when you stomp on the pedal and when you get the power--that's called 'turbo lag'.