A type of jet engine in which a certain portion of the engine's airflow bypasses the combustion chamber.

gas-turbine core jet engine with extra turbine stages driving a large diameter fan which ducts most of the propulsive airflow round a core engine and generates most of the thrust

Gas turbine engine in which a large diameter fan in a short duct generates thrust.

jet engine in which a turbine drives air to the burner

gas-turbine engine with a large diameter cowled fan

A turbofan is a type of airplane engine, similar to a turbojet. It essentially consists of a ducted fan with a smaller diameter turbojet engine mounted behind it that powers the fan. Part of the airstream from the ducted fan passes through the turbojet where it is burnt to power the fan, but the majority of the flow bypasses it, and produces most of the thrust.