Let Me explain you with an example,
Case 1 – we bend our knees while in the process of sitting on the ground with folded legs.
Case 2 – while walking for a long time or after straining our legs a lot, suddenly sometimes we might experience a jerk at the back of our knee and the knee presses back with an acute pain. At this very instant, our knee is unable to sustain our load.
The above-mentioned Case 1 is bending and Case 2 is buckling.
Reiterating this in technical terms, when an object is unable to sustain the load it suddenly collapses and this collapse is termed as buckling. It is a deformation of the member subject to loading that happens in the direction perpendicular to the direction of application of load. Assume the direction of force vertical, then the deformation or buckling will occur in the horizontal direction.
Bending occurs when a force perpendicular to the plane of the object is applied to it.