When people belong to a group, like a school, a team or a family, they feel like they are part of something special and like they have something in common with other members in the group. This feeling is called in-group bias, because people have a bias towards the group they belong to.
On the other hand, people don't have the same feelings or bias towards groups that they don't belong to. This is called out-group bias. People can form opinions about a group that they don't belong to, based on what they hear from others or from news stories. These opinions can be positive or negative.