Plain English Meaning

A jet engine with a big fan up front. Most of the air the fan moves goes around the engine, not through it, which makes the engine quieter and more fuel-efficient than a pure jet.

Full Definition

A turbofan engine is a type of jet engine in which a large fan at the front of the engine pushes a substantial volume of air around the outside of the engine core, while a smaller portion of air passes through the core where it is compressed, mixed with fuel, ignited, and expanded through a turbine. The combined thrust comes from both the bypassed fan air and the hot exhaust from the core. Turbofans are the standard powerplant on most modern airliners and many business jets.