Formal: 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.  https://www.smashingmagazine.com/2014/12/design-principles-visual-weight-direction/

Informal: Having Hierarchy on an element

Project One: Tessellation and Visual Weight