Concave is a term used in mathematics and geometry to describe a shape that curves inward. It can also be used to describe a function that is the negative of a convex function. Here are some key points about concave:

• A concave shape curves inward, like the inside of a bowl.
• A concave function is the negative of a convex function.
• In geometry, a polygon with at least one interior angle greater than 180° is concave.
• A function is called strictly concave if for any two points in the interval and for any , the point on the graph of is above the straight line joining the points and.

Concave is the opposite of convex, which describes shapes that curve outward.