Social identity refers to the way individuals define themselves based on the groups they belong to, such as their nationality, race, religion, or social class. This concept was developed by social psychologists to understand how people's sense of self is influenced by their group memberships and how this affects their attitudes, behaviors, and interactions with others. Social identity theory posits that people derive a sense of self-esteem and belonging from their group memberships, and that this can lead to in-group favoritism and out-group prejudice. Research in this area explores how social identities are formed, how they shape individuals' perceptions and interactions with others, and how they influence societal issues such as intergroup conflict, discrimination, and inequality.