By Blackwell Encyclopedia of Sociology The definition of Blackwell's words, an in-group is an exclusive group that shares common identities and an out-group is a reference of the in-group to those who do do not belong to the group. Because distinct differences between the outgroup and the ingroup are assumed, some people may feel inclined to favor people who belong to the same group as them or who share similar traits. In many cases, especially those involving race and ethnicity, biases often go hand in hand