Complex sentence: Chatham House is the origin of the confidentiality rule known as the Chatham House Rule, which provides that members attending a seminar may discuss the results of the seminar in the outside world, but may not discuss who attended or what they said.
Split into simpler sentences: Chatham House is the origin of an anonymity rule known as the Chatham House Rule. This rule states that members of a seminar may discuss the results of the seminar in the outside world, but may not discuss who attended or what they said.