concave
(adjective)
 curved like the inner surface of a sphere or bowl
Examples of concave in the following topics:
- 
Concavity and the Second Derivative Test
- A related but distinct use of second derivatives is to determine whether a function is concave up or concave down at a point.
 - Specifically, a twice-differentiable function $f$ is concave-up if $f''(x)$ is positive and concave-down if $f''(x)$ is negative.
 - If it is concave-up at the point, it is a minimum; if concave-down, it is a maximum.
 
 - 
Derivatives and the Shape of the Graph
- The shape of a graph may be found by taking derivatives to tell you the slope and concavity.
 - At an inflection point, a function switches from being a convex function to being a concave function or vice versa.
 - Sketch the shape of a graph by using differentiation to find the slope and concavity
 
 - 
Linear Approximation
- If $f$ is concave-down in the interval between $x$ and $a$, the approximation will be an overestimate (since the derivative is decreasing in that interval).
 - If $f$ is concave-up, the approximation will be an underestimate.