Balance is a design principle which could be interpreted in many ways. It could break seen as linear scale:
It could be alignment:
Or even symmetry:
But balance in a design doesn’t need any of that to be balanced. A design could be balanced by being unbalanced!
The idea is to arrange or design a document to create a visual pattern in order to create or keep a balance using line, shape, position and colour. The balance could flow in a horizontal, vertical or radial layout but the idea of balance may not be typically structured. ie. not symmetrical.
The best way to see if a design is balanced is to observe and see if the design tips over in any given way.
Using grids or the idea of symmetrical and asymmetrical positioning is a great and easy way to plan and produce a design with balance but more often then not I find that balance pretty much comes down to a designers gut instinct.