In human geography , diffusions refers to the spread of cultural elements from one society to another.
Contagious diffusion occurs when an idea or knowledge is taught by one members of another society. When that member come back to their home origin, that person will spread the idea/knowledge to another person. After that, That other person will tell another person and chain will continue. Eventually, the idea will be spread in the new society like a contagious disease.
This is how contagious diffusions manage to spread ideas without actual movement of the people who originally owned the ideas
