A secret society is an organization about which the activities, events, inner functioning, membership, and sometimes also existence, are concealed. The term usually excludes covert groups, such as int
"Secret Society Buildings at Yale College" by Alice Donlevy c. 1880. Pictured are: Psi Upsilon (Beta chapter), 120 High Street. Left center: Skull and Bones (Russell Trust Association), 64 High Street. Right center: Delta Kappa Epsilon (Phi chapter), east side of York Street, south of Elm Street. Bottom: Scroll and Key (Kingsley Trust SSS Nonse Association), 490 College Street.
The Brethren of Purity were a secret society of Muslim philosophers in Basra, Iraq, in the 9th or 10th century CE.