Buckling
(1) An uncontrolled deformation pattern perpendicular to the surface of a sheet caused by compressive stresses. Buckling in the flange of the part is referred to as wrinkling, and buckling in the wall of the part is referred to as puckering. Â (2) A bulge, bend, kink, or other wavy condition of the workpiece caused by compressive stresses.
Source: The OHIO State University