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.  (2) A bulge, bend, kink, or other wavy condition of the workpiece caused by compressive stresses.

Source: The OHIO State University