Linked from
The 13 pages that link to Convexity, each with the reason it gives.
Line segmentRelated: Segments provide the defining test for whether a geometric set is convex.
Platonic solidRelated: Convexity excludes indented polyhedra from the Platonic solids.
BetweennessRelated: Convexity is defined through the points lying between pairs of points.
Pasch's theoremRelated: The crossing behavior reflects the convex shape enclosed by a triangle.