Convexity

n. state of being convex, curving outward; convex surface

The word convex means curving out or bulging outward.Convex or convexity may refer to: Mathematics:Convex set, a set of points containing all line segments between each pair of its pointsConvex function, a function with the epigraph (the set of points lying on or above the graph) forming a convex setConvex polygon, a polygon which forms a convex setConvex hull, the minimal convex set containing a set of points XConvex combination, a linear combination of points with non-negative coefficients that sum up to 1Convex conjugate, is a generalization of the Legendre transformationConvex optimization
See more at Wikipedia.org...

Noun
1. the property possessed by a convex shape
(synonym) convexness
(hypernym) shape, form, configuration, contour, conformation
(hyponym) roundedness, bulginess
2. a shape that curves or bulges outward
(synonym) convex shape
(hypernym) solid
(hyponym) umbo

(n.)
The state of being convex; the exterior surface of a convex body; roundness.
  

A convex curve is one where you draw a straight line connecting the end points and the curve falls below the straight line. If the curve is above, it is known as concave.