The Religious Society of Friends is the official name of the religious organization
known as the Quakers
(not to be confused with the defunct
religious group called the Shakers
They started to form in the second half of the 1600's (I'll try to find out more exactly later), as a group against the Church of England. Like many religious minorities in England at the time, many of them fled to The Colonies (as they were known before they became the USA). Fortunately for them, a Quaker happened to own a significant section of land in the new Colonies. His name was William Penn, and his lands eventually became known as Pennsylvania. Another famous Friend was George Fox, who was the source of the name Quakers. There are stories of children carrying on meetings even after all the adults were taken to prison.
The Religious Society of Friends is a Christian group, but with very strong feelings on the importance of tolerance (which influenced the Constitution and the Bill of Rights) and non-violence. They also believe that no man can or should stand between a person and his God, and consider all of their members to be clergy. Their worship is conducted mostly in silence, until someone feels moved to share some words with the group.