Equal distribution of weight.
The two main type of balance are symmetrical and asymmetrical:
Repeating colors, shapes, values, textures, or lines creates a visual relationship between elements, called correspondence.
Treating different elements in the same manner also ties them together. This is called continuity.
When and element is placed in a composition, it creates an implied horizontal and vertical axis at its top, bottom, center and sides. Aligning other elements to these axes creates a visual relationship which unifies them.