Introduction - If you have any usage issues, please Google them yourself
A Convex Hull is the smallest convex polygon that contains every point of the set S. A polygon P is convex if and only if, for any two points A and B inside the polygon, the line segment AB is inside P.
One way to visualize a convex hull is to put a "rubber band" around all the points, and let it wrap as tight as it can. The resultant polygon is a convex hull.