Balance.

http://retaildesignblog.net/category/visual-merchandising/page/13/

When designing a window layout there are certain guidelines and basic rules recommended to follow to ensure the end result is as aesthetically pleasing to the customer as it can be. One of the guidelines recommended, among many, is optical balance. 

Optical balance consists of two main compositions, informal and formal balance. Informal balance being asymmetrical and formal balance symmetrical. Both compositions can be positively effective if presented correctly. 

Balance can be defined as a state of equilibrium or equipoise, therefore formal balance is generally easier to comprehend considering the same objects are used to create a mirror image, however informal balance is still an even distribution of optical weight with various objects. 

The image above represents formal balance while the image below represents informal balance.

http://f-y-n-e.blogspot.ca/

J.Callihoo