Diffusion theory attempts to explain the spread of an innovation through a group or society. Most new products are unsuccessful because they don't find a market. It can attempt to control the spread of their innovation by placing specific types of information in appropriate media at strategic times to reach a specific audience.
Adoption is the acceptance of an innovation by a group member.
Diffusion is the spread of an innovation among a group. Diffusion is a process. It requires key elements to be successful. First, there must be an innovation, something that is perceived as new to that particular group. Second, there must be a series of channels through which the group normally communicates.