High Quality Content by WIKIPEDIA articles! The turbofan or fanjet is a type of airbreathing jet engine that is widely used for aircraft propulsion. The word "turbofan" is a portmanteau of "turbine" and "fan", the turbo portion refers to a gas turbine engine which takes mechanical energy from combustion, and the fan, a ducted fan which uses the mechanical energy from the gas turbine to accelerate air rearwards. The ratio of the mass-flow of air bypassing the engine core compared to the mass-flow of air passing through the core is referred to as the bypass ratio. The engine produces thrust through a combination of these two portions working in concert; engines that use more jet thrust relative to fan thrust are known as low bypass turbofans, while those that have considerably more fan thrust than jet are known as high bypass. Most commercial aviation jet engines in use today are of the high-bypass type, and most modern military fighter engines are low-bypass.