Answer: in-groups and out-groups
Explanation: In-group is a group where two or more individuals who interact with themselves, share the same traits and to which an individual has a feeling of being united, in membership, belonging and close similarities.
Out-group is, therefore, a social group whereby the person doesn't have a feeling of being united, in membership, belonging and close similarities. However, there is always a certainty that individuals will tend to choose and have a natural liking and understanding for their in-group over the out-group.