Inflection point
point on a continuously differentiable plane curve at which the curve crosses its tangent, that is, the curve changes from being concave to convex, or vice versa
An inflection point is a point on a curve where the curve changes from being concave (going up, then down) to convex (going down, then up), or the other way around.
![](http://up.wiki.x.io/wikipedia/commons/7/78/Animated_illustration_of_inflection_point.gif)
![](http://up.wiki.x.io/wikipedia/commons/thumb/0/0f/X_to_the_4th_minus_x.svg/220px-X_to_the_4th_minus_x.svg.png)
An undulation point is like an inflection point but the type of curve doesn't change.