Definitions of diffusion:

• noun:   the spread of social institutions (and myths and skills) from one society to another
• noun:   (physics) the process of diffusing; the intermingling of molecules in gases and liquids as a result of random thermal agitation
• noun:   the property of being diffused or dispersed
• noun:   the act of dispersing or diffusing something

  Example: "The diffusion of knowledge"