Emile Durkheim, a pioneer of the discipline of Sociology, from France introduced the concept of Social fact. In layman’s terms, anything that restricts the activity of the individual from outside is a social fact. A simple example would be Religion, which influences or restricts individual actions in society. Though the concept has been reasonably criticized by later sociologists, it is still relevant today.
One of the most important characteristics of a social fact is Externality, according to Durkheim. Externality means that the social fact exists outside the individual and coming into existence as a part of the autonomous development of society (sui-generis). Thus, any social fact should be developed on its own (say religion, which has a long process of evolution).