The point of contraflexure is the point where: 

Explanation:

• In a bending beam, a point of contraflexure is a location where the bending moment is zero (changes its sign). In a bending moment diagram, it is the point at which the bending moment curve intersects with the zero lines.
• At the point of contraflexure, the bending moment is zero or changes its sign.

For example:

A propped cantilever beam with uniformly distributed load over the entire span

The corresponding BMD is

At distance L/4 from the left support, we get point of contraflexure, as there is the change in sign. At that point, the Bending moment is zero.