Plain English Meaning
Curving inward. The surface dips in, the way the inside of a spoon does.
Full Definition
Curved inward, like the inside of a bowl. In airfoil design, a concave surface curves away from the oncoming airflow, forming a hollow rather than a bulge.
Context Anchor
Seen in airfoil shape discussions when describing the curved surfaces of a wing cross-section.
Derivation
From Latin concavus, meaning 'hollow' or 'arched inward.' The 'cav' part is the same root as 'cave' — a hollowed-out space. That image of a hollow curve is exactly what concave means in airfoil shape.
Why Pilots Care
Concave lower surfaces on airfoils can increase lift at low speeds but may alter stall behavior and drag.