Definition
A jet engine that uses a large fan at the front to move a high volume of air. Some of that air passes through the engine core, where it is compressed, mixed with fuel, ignited, and expelled as hot exhaust. The rest of the air bypasses the core and is accelerated by the fan alone. Thrust is produced by combining the bypass airflow with the core exhaust.
Plain English
A jet engine with a big fan at the front. Some of the air goes through the hot middle of the engine to be burned with fuel, and some of it is pushed around the outside by the fan. Both streams together push the airplane forward.
Context Anchor
Seen in jet engine basics, aircraft systems descriptions, and preflight discussions of jet engine inlets.
Derivation
From 'turbo' (turbine, the spinning bladed wheel inside the engine) and 'fan' (the large bladed wheel at the front). The name describes exactly what the engine is: a turbine-driven engine with an added fan that moves bypass air around the core.
Why Pilots Care
Powers most commercial airliners and many business jets, delivering better fuel economy, lower noise, and reliable thrust across a wide speed range.
Intuition Check
Do not think of the fan as a separate household-style fan added to an engine. In a turbofan engine, the fan is part of the jet engine system and is driven by the engine’s turbine.
Example Sentence 1
The aircraft is powered by two turbofan engines mounted under the wings.
Example Sentence 2
During the climb, the turbofan engine maintained efficient thrust while keeping fuel flow within limits.