Every element on a web page exerts a visual force that attracts the eye of the viewer. The greater the force, the more the eye is attracted. These forces also appear to act on other elements, imparting a visual direction to their potential movement and suggesting where you should look next.
We refer to this force as visual weight and to the perceived direction of visual forces as visual direction. Both are important concepts to understand if you want to create hierarchy, flow, rhythm and balance in your composition.