The paper is a theoretical review of “social movement” term definitions. Aiming to show differences among definitions within different paradigms and scientific evolution of the term the main approaches of defining social movements are discussed. Initially, social movements were studied by psychologists, who were examining different forms of collective behavior, such as mobs, crowds, protests and etc. Most of them considered social movements as an irrational and destructive form of collective action driven by the instincts of people. During the next decades, the theory of social movements was developed mostly by sociologists who, on the contrary, started to seek social reasons inducing this type of collective action. Different theoretical schools proposed various concepts of explaining the origin of social movements, but all of them agreed on the main characteristics: rational and organized collective action driven by unfulfilled social needs. Different authors linked social movement definitions with other important social phenomena such as norms and values, social conflict, social identity, and social network. Political scientists have also contributed to the study of social movements but in terms of power and state, terrorism and violence. Discussing psychological, sociological, and political science approaches to term definition we came to the conclusion that the most inclusive sociological definition is viewing social movement as a social network through which collective action is performed to achieve total or partial social change. Such kind of definition makes it possible to reveal the main criteria necessary to distinguish social movement as a separate social phenomenon from other types of collective action.