##### Wiktionary

**inflection point**

n. (context mathematics English) a point of inflection

##### Wikipedia

**Inflection point**

In differential calculus, an **inflection point**, **point of inflection**, **flex**, or **inflection** (**inflexion**) is a point on a curve at which the curve changes from being concave (concave downward) to convex (concave upward), or vice versa.

A point where the curvature vanishes but does not change sign is sometimes called a **point of undulation** or **undulation point**.

In algebraic geometry an inflection point is defined slightly more generally, as a point where the tangent meets the curve to order at least 3, and an undulation point or **hyperflex** is defined as a point where the tangent meets the curve to order at least 4.