Convex :
1. Said of a curve that bulges toward some reference point, usually the horizontal axis or the origin of a diagram. More formally, a curve is convex from below (or convex to something below it) if all straight lines connecting points on it lie on or above it. Contrasts with concave.
2. Said of a set that contains all straight line segments joining points within it.
(Deardorff’s Glossary of International Economics)
