Skulls and bones

The Order of Skull and Bones, a Yale University society, was originally known as the Brotherhood of Death. It is one of the oldest student secret societies in the United States. It was founded in 1832 and membership is open to an elite few. The society uses masonic inspired rituals to this day. Members meet every Thursday and Sunday of each week in a building they call the “Tomb”.
According to Judy Schiff, Chief Archivist at the Yale University Library, the names of the members were not kept secret until the 1970s, but the rituals always have been. Both of the Bush presidents were members of the society while studying at Yale, and a number of other members have gone on to great fame and fortune.
The society is surrounded by conspiracy theories; the most popular of which is probably the idea that the CIA was built on members from the group. The CIA released a statement in 2007 (coinciding with the popularity of the film The Good Shepherd) in which it denied that the group was an incubator for the CIA.

What is a secret societey ?

A secret society is a social organization that 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 often sworn to hold the society's secrets by an oath. The term "secret society" is often used to describe fraternal organizations (e.g. Freemasonry) 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 immensely powerful, with self-serving financial or political agendas, global reach, and often satanic beliefs.