taboo

A taboo, also spelled tabu, is a social group's ban, prohibition, or avoidance of something (usually an utterance or behavior) based on the group's sense that it is excessively repulsive, offensive, sacred, or allowed only for certain people. Such prohibitions are present in virtually all societies. Taboos may be prohibited explicitly, for example within a legal system or religion, or implicitly, for example by social norms or conventions followed by a particular culture or organization.