Mass psychology is the study of how individual thoughts, feelings, and behaviors are influenced by large groups of people. It examines how social dynamics, such as group identity and peer pressure, can shape opinions and actions. This field helps explain phenomena like crowd behavior, social movements, and the spread of fads. Researchers in mass psychology analyze factors like emotional contagion and groupthink, which can lead to collective decision-making that differs from individual reasoning. Understanding these concepts is crucial for fields such as marketing, political science, and sociology, as they reveal how public sentiment can be swayed and mobilized.