Social group is a term in the social sciences field that simply means a set of people (two or more) who communicate with each other. Though it has a concise definition, the concept gets more complex and subjective once one starts analyzing what it means to communicate.
Some theorists hold that social groups are highly unified and value-based, forming wherever people mutually recognize that they share aspirations, interests, motives, and backgrounds. These thinkers conceive of socialization as a process that strengthens the individual's sense of self by ascribing to it models and values that it sees in life.
Other thinkers believe that social groups are much more loose and contingent. As evidence, they often point at socialization on the internet, where social groups emerge despite highly imperfect and dubious information (for example, online forums, where an individual can "enter" a social group without any identity, and can refashion his or her presented identity at will).
Despite these different conceptions of social cohesion, it is generally agreed that social groups require some kind of shared topical or attitudinal affinity to stay in place for long. Therefore, one of the best measures for a social group's cohesive strength is its duration.