Buckling

A structural instability phenomenon in which a member subjected to compressive (or certain shear) loads suddenly deforms laterally or out of its original plane when the applied load reaches a critical value, often with a mode shape and rapid loss of load‑carrying capacity.

A stability-related failure phenomenon in which a structural element subjected to compressive or otherwise destabilizing loads experiences a sudden lateral or out-of-plane deflection at a critical load, causing a rapid change in geometry and reduction or loss of load-carrying capacity.