1. A primary group is typically a small group of individuals with an enduring personal relationship to one another, e.g. parents, spouse or close friends (Elwell).
2. A secondary group is a group of individuals who do not know each other on a personal level but interact in pursuit of a common goal (Elwell).
3. An In-group is a social group an individual belongs to and identifies with (Elwell). In-groups often foster ethnocentrism, and have a "we versus they" attitude (Groups). Members have a feeling of distinctiveness and superiority over those not in their group.
4. An Out-group is a social group toward which one feels competition or opposition (Brussiere).
5. A reference group is any group used to evaluate oneself (Groups). It does not necessarily have to be a group you belong to. It is a group people draw on for the social norms which give order and meaning to their lives (Major).
6. A Social Network is a group of people interact with for various purposes but with no emotional attachment.
Primary group: Members of a primary group tend to interact on an intimate basis (face-to-face, phone, email, etc), and share social solidarity of long-standing (Major). They perform functions such as production, reproduction, socialization, education, and enforcing social discipline. Primary groups extend to include the community and voluntary organizations to which people may belong.
Secondary group: There is no emotional commitment between members of the group and