Definition: The point of contraflexure (also called the point of inflexion) is the location along a beam where the bending moment changes sign — passing from positive (sagging) to negative (hogging) or vice versa. Because the bending moment is continuous, changing sign means it must pass through zero at that point.

Physical meaning: Bending moment governs the curvature of the deflected beam through M = EI·(d²y/dx²). Where M is positive the beam curves one way (concave up, sagging); where M is negative it curves the other way (concave down, hogging). At the point of contraflexure the curvature reverses, so the deflected shape changes from concave to convex. This is exactly why it is called a point of inflexion. Such points typically occur in overhanging beams and continuous beams, where both sagging and hogging regions exist; the number of contraflexure points depends on the loading and support arrangement.

Why the other options are wrong:

• Shear force is zero — this identifies the point of maximum (or minimum) bending moment, because dM/dx = V (shear force), so M is stationary where V = 0. That is a different point entirely from where M changes sign.
• Load intensity is zero — load intensity w relates to the second derivative of moment (d²M/dx² = −w) and does not define where the moment changes sign; a beam can carry zero load intensity over a span without any contraflexure there.
• Bending moment is maximum — at the contraflexure point the bending moment is actually zero, the opposite of maximum; the maximum occurs where the shear force is zero.