A secret society is an organization which requires its members to conceal certain activities, such as rites of initiation or club ceremonies—from outsiders. Members may be required to conceal or deny their membership, and are sometimes sworn to hold the society's secrets by oath

The term "secret society" is often used to describe fraternal organizations that may have secret ceremonies, but is also commonly applied to organizations ranging from the common and innocuous (collegiate fraternities) to mythical organizations described in conspiracy theories as influencial, with self-serving financial or political agendas, global reach, and sometimes religious, esoteric, including satanic beliefs.