In-group bias is a phenomenon in which people favor members of their own social group over those outside of it. This bias can manifest in many ways, from preferential treatment to prejudice. Understanding the power of social groups is essential to understanding how in-group
From Wikipedia
In-group favoritism, sometimes known as in-group–out-group bias, in-group bias, intergroup bias, or in-group preference, is a pattern of favoring members of one's in-group over out-group members. This can be expressed in the evaluation of others via the ultimate attribution error, in the allocation of resources, and in many other ways.