Balance

Every image or element you place on a page hold a certain weight. Bigger objects appear heavy, small objects appear light, it is your job to find the right amount of elements to use to keep the weight evenly distributed.

(simple example balance, an image I made for a beginner's art class)

Symmetrical Balance is when two images mirror each other. This type really isn't seen in web design.

Horizontal Symmety is ideal for creating web pages because you can create balanced columns. Pages have a balcnced center to create a clean cut feel:

Asymmetrical Balance is informal, abstract and visually interesting: