Early builders of turbochargers called them as "turbosuperchargers". A supercharger is an air compressor used for forcing air into an engine. They thought that by adding a turbine to turn the supercharger, it would yield a "turbosupercharger". The term was soon shortened to "turbocharger". This can now create some confusion. The term "turbosupercharged" is sometimes used to refer to an engine that uses both a crankshaft-driven supercharger and an exhaust-driven turbocharger. This is also called twincharging.