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Opposite of concave . A geometric shape is convex if all its edges point outwards. That is no part of it curves or faces inwards. If a shape is convex, a line segment drawn between any two points on the shape will always lie inside the shape. The figure above is a convex pentagon. No part of it is caved in and any line segment, such as the red one shown, linking two points on it always lies inside the shape. See also Concave definition.
Concave = hollowed or rounded inward. Convex = curved or rounded outward. If the moving joint surface is CONVEX, sliding is in the OPPOSITE direction of the angular movement of the bone. If the moving joint surface is CONCAVE, sliding is in the SAME direction as the angular movement of the bone.