Any convex body or surface.
Curved or bowed outward like the outside of a bowl or sphere or circle
(of a set in Euclidean space) arranged such that for any two points in the set, a straight line between the two points is contained within the set.
(of a polygon) having no internal angles greater than 180 degrees.
(of a real-valued function on the reals) having an epigraph which is a convex set.