The wall of the part curves inwards.

a shape that curves or bends inward

Hollowed or rounded inward. Causes shadows on the surface of teeth.

A concave surface, or the space bounded by it; the state of being concave.

a polygon bounded by the CP and the minimal-area convex polygon which circumscribes it (its convex hull )

A weld that falls below the intended perpendicular plane.

the property possessed by a concave shape