The "Diffusion of Innovations" is a theory that explains how new ideas, products, or technologies spread within a society or from one society to another. It identifies several key factors that influence this process, including the innovation's perceived advantages, compatibility with existing values, complexity, trialability, and observability. The theory categorizes adopters into five groups: innovators, early adopters, early majority, late majority, and laggards. Each group has different characteristics and motivations for adopting innovations, which affects the overall rate of adoption and the eventual success of the innovation in the market.