What is the major characteristic of a social group

The major characteristic of a social group is the existence of a common identity and values between its members.

Explanation:

A social group is a collection of two or more people who interact with each other. This may be because they identify with each other or because they have a common goal. Often there will be a social identity, the consciousness of belonging to a certain group and being treated as such by others. That group has a (desired) self-image and is distinguished as unique by others. The self-image does not have to correspond to the image that outsiders have of a group, which is often characterized by stereotypes.

People often form part of several social groups, whereby a distinction is made between primary and secondary groups. In the first, members maintain personal and lasting relationships, while in the second, the relationship is more formal and focused. Secondary groups can also be much larger.

Every group has a social structure in which everyone has a social position and role. With each role a certain behavior is expected according to certain social conventions. Compliance with this is reinforced by social control and internalization, the process by which people acquire certain social rules, so that over time these rules are no longer considered as externally imposed rules, but as guidelines that they themselves have chosen. This also determines social behavior.  

However, values vary between societies, but also within, for example, social classes. In addition, values vary over time while a society develops. Deviant behavior, non-compliance with certain standards, can influence social status and acceptance and even lead to exclusion.