Shunning can be the act of social rejection, or mental rejection. Social rejection is when a person or group deliberately avoids association with, and habitually keeps away from an individual or group. This can be a formal decision by a group, or a less formal group action which will spread to all members of the group as a form of solidarity. It is a sanction against association, often associated with religious groups and other tightly knit organizations and communities. Targets of shunning can include persons who have been labeled as, apostates, whistleblowers, dissidents, scabs, or anyone the group perceives as a threat or source of conflict. Social rejection has been established to cause psychological damage and has been categorized as torture. Mental rejection is a more individual action, where a person subconsciously or willfully ignores an idea, or a set of information related to particular viewpoint. Some groups are made up of people who shun the same ideas.
Social rejection was and is a punishment used by many customary legal systems. Such sanctions include the ostracism of ancient Athens and the still-used kasepekang in Balinese society.