Convex:

A set is convex if, given two points in the set, the straight line segment joining the two points is also contained in the set.

For example, a circular disk is convex, as is a solid sphere, or a solid cube. A torus is not convex, however, since the line segment joining points on opposite sides of the "hole" is not entirely contained in the torus itself.

See also:

Convex Hull

Convex Envelope

8/12/94 dpvc@geom.umn.edu -- The Geometry Center