Most of the social changes in all known societies have developed through diffusion; they spread of culture traits from group to group. Diffusion operates both within societies and between societies, for example, democracy and jazz (which originated among black musicians of New Orleans).
Diffusion takes place whenever societies come into contact. Ralph Linton, in a famous passage has tried to show how all Americans have actually borrowed most of their cultures from other societies.
Diffusion is a two-way process, a selective process, and it generally involves some modifications of the borrowed element.