An aerofoil is an aerodynamic device shaped so that air flowing over one side is accelerated compared to air flowing over the other side. The faster-flowing air has lower pressure, which generates a force on the aerofoil which acts in a direction towards the side with the faster air flow.

In an aircraft wing, the aerofoil is arranged with the faster airflow on top, so that the force generated is upward lift. In automotive applications an aerofoil is mounted upside down, so that it generates downforce.